[XFS] Make the bulkstat_one compat ioctl handling more sane

Currently the compat formatter was handled by passing
in "private_data" for the xfs_bulkstat_one formatter,
which was really just another formatter... IMHO this
got confusing.

Instead, just make a new xfs_bulkstat_one_compat
formatter for xfs_bulkstat, and call it via a wrapper.

Also, don't translate the ioctl nrs into their native
counterparts, that just clouds the issue; we're in a
compat handler anyway, just switch on the 32-bit cmds.

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