internal/netreflect: don't build on go1.9 or above

This package doesn't work with Go 1.9 or above.
The bypass surgery for grafting the net and internal/poll packages of
Go 1.9 starts with disabling this packge.

Updates golang/go#19051.

Change-Id: I82d742d267f155cf440884e845b24402a5a5bfdf
Reviewed-on: https://go-review.googlesource.com/37034
Reviewed-by: Ian Lance Taylor <iant@golang.org>

internal/netreflect/socket.go

@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !go1.9
+
 // Package netreflect implements run-time reflection for the
 // facilities of net package.
+//
+// This package works only for Go 1.8 or below.
 package netreflect
 
 import (

internal/netreflect/socket_posix.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !go1.9
 // +build darwin dragonfly freebsd linux netbsd openbsd solaris windows
 
 package netreflect

internal/netreflect/socket_stub.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !go1.9
 // +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
 
 package netreflect

internal/netreflect/socket_test.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !go1.9
 // +build darwin dragonfly freebsd linux netbsd openbsd solaris windows
 
 package netreflect_test