Add internal_ipv6_range to local.network variable in net-vpc module

[kaysalawu]

The output variable below does not work because the key internal_ipv6_range does not exist in local.network in main.tf

output "internal_ipv6_range" {
  description = "ULA range."
  value       = try(local.network.internal_ipv6_range, null)
}

The correct code should be:

locals {
  network = (
    var.vpc_create
    ? {
      id                  = try(google_compute_network.network[0].id, null)
      name                = try(google_compute_network.network[0].name, null)
      self_link           = try(google_compute_network.network[0].self_link, null)
      **internal_ipv6_range = try(google_compute_network.network[0].internal_ipv6_range, null)**
    }
...
}