Correct behavior of enable_l4_ilb_subsetting for clusters

Author: AndreasBergmeier6176

tf/service_cluster/container.tf

@@ -59,6 +59,9 @@ resource "google_container_cluster" "main" {
 
   private_ipv6_google_access = var.private_ipv6_google_access
 
+  # Seems like backend enforces subsetting on dual stack
+  enable_l4_ilb_subsetting = var.ip_allocation_policy == "IPV4_IPV6"
+
   lifecycle {
     ignore_changes = [
       dns_config,