Some filesystems would like to keep private information together with each
dquot. Add callbacks alloc_dquot and destroy_dquot allowing filesystem to
allocate larger dquots from their private slab in a similar fashion we
currently allocate inodes.
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NMark Fasheh <mfasheh@suse.com>