64bit atomics are broken on 32bit systems. This is issue 599.

linux/arm builders all broke with this change, I am concerned that the other 32bit builders are silently impacted.

««« original CL description
net: fix data races on deadline vars

Fixes #4434.

R=mikioh.mikioh, bradfitz, dvyukov, alex.brainman
CC=golang-dev
https://golang.org/cl/6855110
»»»

R=rsc, mikioh.mikioh, dvyukov, minux.ma
CC=golang-dev
https://golang.org/cl/6852105