Only detecting stale connections for UDP ports in kube-proxy.

The detectStaleConnections function in kube-proxy is very expensive in
terms of CPU utilization. The results of this function are only actually
used for UDP ports. This adds a protocol attribute to ServicePortName to
make it simple to only run this function for UDP connections. For
clusters with primarily TCP connections this can improve kube-proxy
performance by 2x.

pkg/proxy/types.go

@@ -43,7 +43,8 @@ type Provider interface {
 // identifier for a load-balanced service.
 type ServicePortName struct {
 	types.NamespacedName
-	Port string
+	Port     string
+	Protocol v1.Protocol
 }
 
 func (spn ServicePortName) String() string {