xfs: verify COW extent size hint is valid in inode verifier

There are rules for vald extent size hints. We enforce them when
applications set them, but fuzzers violate those rules and that
screws us over. Validate COW extent size hint rules in the inode
verifier to catch this.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>