net: make windows (*netFD).connect work like its unix version
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.