net: enable runtime-integrated network pollster on freebsd/arm

Fixes #6146.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/12927048

src/pkg/net/fd_bsd.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 freebsd,arm
+// +build ignore
 
 // Waiting for FDs via kqueue/kevent.
 

src/pkg/net/fd_poll_runtime.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 darwin freebsd,amd64 freebsd,386 linux netbsd openbsd windows
+// +build darwin freebsd linux netbsd openbsd windows
 
 package net
 

src/pkg/net/fd_poll_unix.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 freebsd,arm
+// +build ignore
 
 package net