target/tcm_loop: Use target_submit_tmr() instead of open-coding this function

Use target_submit_tmr() instead of open-coding this function. The
only functional change is that TMFs are now added to sess_cmd_list,
something the current code does not do. This behavior change is a
bug fix because it makes LUN RESETs wait for other TMFs that are in
progress for the same LUN.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: David Disseldorp <ddiss@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>