Do generic processing even for drivers which define .bdrv_check_perm
handler. It's needed for further preallocate filter: it will need to do
additional action on bdrv_check_perm, but don't want to reimplement
generic logic.

The patch doesn't change existing behaviour: the only driver that
implements bdrv_check_perm is file-posix, but it never has any
children.

Also, bdrv_set_perm() don't stop processing if driver has
.bdrv_set_perm handler as well.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201021145859.11201-8-vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>