ext4: Make sure quota files are not grabbed accidentally

If ext4 filesystem is corrupted so that quota files are linked from
directory hirerarchy, bad things can happen. E.g. quota files can get
corrupted or deleted. Make sure we are not grabbing quota file inodes
when we expect normal inodes.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20210812133122.26360-1-jack@suse.cz