unix: fix cmsg alignment on aix
unix: fix cmsg alignment on aix

This was missing from CL 171941.

Change-Id: I14f16355b2fe18103d2713faf2bebf004248fc0c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/172257
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

multiplay/golang-sys,golang/sys,multiplay/golang-sys,multiplay/golang-sys,golang/sys,multiplay/golang-sys,golang/sys