[XFS] Reorder xfs_ioctl32.c for some tidiness

Put things in IMHO a more readable order, now
that it's all done; add some comments.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>