Enable AWS NLB cross-zone load balancing

* https://github.com/terraform-providers/terraform-provider-aws/pull/3537
* https://aws.amazon.com/about-aws/whats-new/2018/02/network-load-balancer-now-supports-cross-zone-load-balancing/

aws/container-linux/kubernetes/workers/ingress.tf

@@ -5,6 +5,8 @@ resource "aws_lb" "ingress" {
   internal           = false
 
   subnets = ["${var.subnet_ids}"]
+
+  enable_cross_zone_load_balancing = true
 }
 
 # Forward HTTP traffic to workers