syscall: use correct cmsg alignment for netbsd/arm64
syscall: use correct cmsg alignment for netbsd/arm64

netbsd/arm64 requires 128-bit alignment for cmsgs.

Re-submit of CL 258437 which was dropped due to #41718.

Change-Id: I898043d79f513bebe1a5eb931e7ebd8e291a5aec
Reviewed-on: https://go-review.googlesource.com/c/go/+/258677
Trust: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Trust: Benny Siegert <05f4aee36fd25d0de2a07789fd6e73398db492cc@gmail.com>
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Benny Siegert <05f4aee36fd25d0de2a07789fd6e73398db492cc@gmail.com>

CAFxX/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go