Correct handling of network ACL default IPv6 ingress/egress rules

[ewbankkit]

Fixes #12831.

• Handle IPv6 default rules the same as IPv4 default rules
• A NACL only has IPv6 default rules if the associated VPC has an IPv6 CIDR block, so in the aws_default_network_acl resource acceptance tests make the number of hidden rules a variable

Acceptance tests:

make testacc TEST=./builtin/providers/aws/ TESTARGS='-run=TestAccAWSDefaultNetworkAcl_basicIpv6Vpc'
make testacc TEST=./builtin/providers/aws/ TESTARGS='-run=TestAccAWSNetworkAcl_ipv6VpcRules'

[stack72]

LGTM! Thanks for picking this up - sorry i didn't add this when i added the IPv6 work

% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSDefaultNetworkAcl_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/03/25 23:28:32 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSDefaultNetworkAcl_ -timeout 120m
=== RUN   TestAccAWSDefaultNetworkAcl_basic
--- PASS: TestAccAWSDefaultNetworkAcl_basic (50.56s)
=== RUN   TestAccAWSDefaultNetworkAcl_basicIpv6Vpc
--- PASS: TestAccAWSDefaultNetworkAcl_basicIpv6Vpc (36.87s)
=== RUN   TestAccAWSDefaultNetworkAcl_deny_ingress
--- PASS: TestAccAWSDefaultNetworkAcl_deny_ingress (51.55s)
=== RUN   TestAccAWSDefaultNetworkAcl_SubnetRemoval
--- PASS: TestAccAWSDefaultNetworkAcl_SubnetRemoval (92.68s)
=== RUN   TestAccAWSDefaultNetworkAcl_SubnetReassign
--- PASS: TestAccAWSDefaultNetworkAcl_SubnetReassign (109.93s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	341.606s

[ghost]

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