loop: move updating lo_flags out of loop_set_status_from_info

While loop_configure simplify assigns the flags passed in by userspace,
loop_set_status only looks at the two changeable flags, and currently
has to do a complicate dance to implement that.

Move assign lo->lo_flags out of loop_set_status_from_info into the
callers and thus drastically simplify the lo_flags handling in
loop_set_status.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250110073750.1582447-2-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>