BACKPORT: loop: Call loop_config_discard() only after new config is applied

loop_set_status() calls loop_config_discard() to configure discard for
the loop device; however, the discard configuration depends on whether
the loop device uses encryption, and when we call it the encryption
configuration has not been updated yet. Move the call down so we apply
the correct discard configuration based on the new configuration.

Signed-off-by: Martijn Coenen <maco@android.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 7c5014b0987a30e4989c90633c198aced454c0ec)
Bug: 148607611
Change-Id: I77cb81b7c8038ebdb2d4cd6161c034a9e94cf516