include: detect corrupt frag from byteswap

include: detect corrupt frag from byteswap

If a big-endian MDS writes frag_t values into the metadata pool, these
will persist and confuse the MDS after it tries properly parsing them as
little-endian. Fortunately detecting this situation is fairly easy as we
restrict the number of bits and the number of bits restricts the mask
value.

Fixes: https://tracker.ceph.com/issues/73792
Signed-off-by: Patrick Donnelly <pdonnell@ibm.com>
(cherry picked from commit 6bf91e4f6e49d99711b8be845eb77c883d662704)