Added support for `ipv6_cidr_block` in network acls (#329)

Add support for `ipv6_cidr_block` in `*_{in|out}bound_acl_rules`.  As a
conseqeunce, the (ipv4) `cidr_block` is made optional.

main.tf

@@ -555,7 +555,8 @@ resource "aws_network_acl_rule" "public_inbound" {
   icmp_code       = lookup(var.public_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.public_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.public_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.public_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.public_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.public_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "public_outbound" {
@@ -571,7 +572,8 @@ resource "aws_network_acl_rule" "public_outbound" {
   icmp_code       = lookup(var.public_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.public_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.public_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.public_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.public_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.public_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 #######################
@@ -605,7 +607,8 @@ resource "aws_network_acl_rule" "private_inbound" {
   icmp_code       = lookup(var.private_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.private_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.private_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.private_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.private_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.private_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "private_outbound" {
@@ -621,7 +624,8 @@ resource "aws_network_acl_rule" "private_outbound" {
   icmp_code       = lookup(var.private_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.private_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.private_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.private_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.private_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.private_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 ########################
@@ -655,7 +659,8 @@ resource "aws_network_acl_rule" "intra_inbound" {
   icmp_code       = lookup(var.intra_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.intra_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.intra_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.intra_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.intra_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.intra_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "intra_outbound" {
@@ -671,7 +676,8 @@ resource "aws_network_acl_rule" "intra_outbound" {
   icmp_code       = lookup(var.intra_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.intra_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.intra_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.intra_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.intra_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.intra_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 ########################
@@ -705,7 +711,8 @@ resource "aws_network_acl_rule" "database_inbound" {
   icmp_code       = lookup(var.database_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.database_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.database_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.database_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.database_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.database_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "database_outbound" {
@@ -721,7 +728,8 @@ resource "aws_network_acl_rule" "database_outbound" {
   icmp_code       = lookup(var.database_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.database_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.database_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.database_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.database_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.database_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 ########################
@@ -755,7 +763,8 @@ resource "aws_network_acl_rule" "redshift_inbound" {
   icmp_code       = lookup(var.redshift_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.redshift_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.redshift_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.redshift_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.redshift_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.redshift_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "redshift_outbound" {
@@ -771,7 +780,8 @@ resource "aws_network_acl_rule" "redshift_outbound" {
   icmp_code       = lookup(var.redshift_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.redshift_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.redshift_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.redshift_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.redshift_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.redshift_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 ###########################
@@ -805,7 +815,8 @@ resource "aws_network_acl_rule" "elasticache_inbound" {
   icmp_code       = lookup(var.elasticache_inbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.elasticache_inbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.elasticache_inbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.elasticache_inbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.elasticache_inbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.elasticache_inbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 resource "aws_network_acl_rule" "elasticache_outbound" {
@@ -821,7 +832,8 @@ resource "aws_network_acl_rule" "elasticache_outbound" {
   icmp_code       = lookup(var.elasticache_outbound_acl_rules[count.index], "icmp_code", null)
   icmp_type       = lookup(var.elasticache_outbound_acl_rules[count.index], "icmp_type", null)
   protocol        = var.elasticache_outbound_acl_rules[count.index]["protocol"]
-  cidr_block  = var.elasticache_outbound_acl_rules[count.index]["cidr_block"]
+  cidr_block      = lookup(var.elasticache_outbound_acl_rules[count.index], "cidr_block", null)
+  ipv6_cidr_block = lookup(var.elasticache_outbound_acl_rules[count.index], "ipv6_cidr_block", null)
 }
 
 ##############