go.net/ipv6: add stubs for nacl build

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/98440046

ipv6/control_rfc3542_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6
 

ipv6/dgramopt_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6
 

ipv6/genericopt_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6
 

ipv6/helper_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6
 

ipv6/icmp_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6
 

ipv6/payload_cmsg.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !plan9,!windows
+// +build !nacl,!plan9,!windows
 
 package ipv6
 

ipv6/payload_noncmsg.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 windows
+// +build nacl plan9 windows
 
 package ipv6
 

ipv6/sockopt_rfc3542_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build plan9 solaris
+// +build nacl plan9 solaris
 
 package ipv6