enable_ipv6 without create_ipv6_address or ipv6_address creates ipv4 frontends

[anuraaga]

TL;DR

When setting enable_ipv6 without create_ipv6_address or ipv6_address, frontends are still made with ephemereal IPV4 addresses.

Expected behavior

I was expecting create_ipv6_address to be enabled by default when enabling ipv6. If not desired, then this case should be treated as an error.

Observed behavior

Two frontends labeled name-ipv6-http(s) with IPV4 addresses

Terraform Configuration

Obvious from description

Terraform Version

1.5.7

Additional information

The issue is local.ipv6_address is undefined in this case as both vars aren't set

https://github.com/terraform-google-modules/terraform-google-lb-http/blob/master/main.tf#L20

When used below in the forwarding rules, it is passed as undefined, which causes global_fowarding_rule to allocate an ephemereal IPV4 address

https://github.com/terraform-google-modules/terraform-google-lb-http/blob/master/main.tf#L75