Move userspace code to sub-package in proxy.

Moves the userspace code in proxy to a sub-package and adds the
ProxyProvider interface.

This is in preparation for landing an implementation of
https://github.com/GoogleCloudPlatform/kubernetes/issues/3760, which
will mostly be in another sub package for iptables.

pkg/proxy/userspace/loadbalancer.go

@@ -0,0 +1,33 @@
+/*
+Copyright 2014 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package userspace
+
+import (
+	"net"
+
+	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/proxy"
+)
+
+// LoadBalancer is an interface for distributing incoming requests to service endpoints.
+type LoadBalancer interface {
+	// NextEndpoint returns the endpoint to handle a request for the given
+	// service-port and source address.
+	NextEndpoint(service proxy.ServicePortName, srcAddr net.Addr) (string, error)
+	NewService(service proxy.ServicePortName, sessionAffinityType api.ServiceAffinity, stickyMaxAgeMinutes int) error
+	CleanupStaleStickySessions(service proxy.ServicePortName)
+}