CL 17821 used syscall.CancelIoEx to cancel outstanding connect
call, but did not check for syscall.CancelIoEx return value.
Also I am worried about introducing race here. We should use
proper tools available for us instead. For example, we could
use fd.setWriteDeadline just like unix version does. Do that.

Change-Id: Idb9a03c8c249278ce3e2a4c49cc32445d4c7b065
Reviewed-on: https://go-review.googlesource.com/17920Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>