cmd/coordinator: preserve source IPs on our load balancer

Change-Id: I2b8f004b3b06d83e97b217aac6cfda2b35e518c3
Reviewed-on: https://go-review.googlesource.com/c/build/+/174084
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/cmd/coordinator/service-prod.yaml b/cmd/coordinator/service-prod.yaml
index d2a773e..010a6ef 100644
--- a/cmd/coordinator/service-prod.yaml
+++ b/cmd/coordinator/service-prod.yaml
@@ -17,3 +17,4 @@
     app: coordinator
   type: LoadBalancer
   loadBalancerIP: 107.178.219.46
+  externalTrafficPolicy: Local