net: eliminate odd if statement with identical branches

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/7447044

Committer: Ian Lance Taylor <iant@golang.org>
runtime: add atomics to fix arm

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7429046
build: skip cgo test on arm

Update issue 4961.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/7451044