net, syscall: add missing copyright notices

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5375099
diff --git a/src/pkg/net/pipe.go b/src/pkg/net/pipe.go
index b99e6e6..0ce7ccb 100644
--- a/src/pkg/net/pipe.go
+++ b/src/pkg/net/pipe.go
@@ -1,3 +1,7 @@
+// Copyright 2010 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.
+
 package net
 
 import (