net: prevent spurious on-connect events via epoll on linux
On Linux, adding a socket descriptor to epoll instance before getting
the EINPROGRESS return value from connect system call could be a root
cause of spurious on-connect events.
See golang.org/issue/8276, golang.org/issue/8426 for further information.
All credit to Jason Eggleston <jason@eggnet.com>
Fixes #8276.
Fixes #8426.
LGTM=dvyukov
R=dvyukov, golang-codereviews, adg, dave, iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/
120820043