update kcp-go package

vendor/golang.org/x/net/ipv6/control_stub.go

@@ -0,0 +1,13 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
+
+package ipv6
+
+import "golang.org/x/net/internal/socket"
+
+func setControlMessage(c *socket.Conn, opt *rawOpt, cf ControlFlags, on bool) error {
+	return errOpNoSupport
+}