icmp: don't fail test on JS

Change-Id: I653cd92dc1b114719d1b6f3e296f67ed30edff24
Reviewed-on: https://go-review.googlesource.com/121555
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

icmp/listen_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 nacl plan9
+// +build js nacl plan9
 
 package icmp
 

icmp/message.go

@@ -25,7 +25,7 @@ import (
 	"golang.org/x/net/ipv6"
 )
 
-// BUG(mikio): This package is not implemented on NaCl and Plan 9.
+// BUG(mikio): This package is not implemented on JS, NaCl and Plan 9.
 
 var (
 	errMessageTooShort  = errors.New("message too short")