maintainers: Add myself as a NetBSD reviewer

I volunteer to review NetBSD patches.
Adding myself will help to not miss some of them.

Restore NetBSD as a maintained host.

All patches to make qemu/pkgsrc building have been emitted to review.

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Message-id: 20170513022143.2838-1-n54@gmx.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>