Add TCP Healthcheck

pkg/server/service/loadbalancer/hrw/hrw.go

@@ -39,6 +39,7 @@ type Balancer struct {
 	status map[string]struct{}
 	// updaters is the list of hooks that are run (to update the Balancer
 	// parent(s)), whenever the Balancer status changes.
+	// No mutex is needed, as it is modified only during the configuration build.
 	updaters []func(bool)
 	// fenced is the list of terminating yet still serving child services.
 	fenced map[string]struct{}