target: Fix handling of aborted commands

- If we stop processing an already-aborted command in
  target_execute_cmd(), then we need to complete t_transport_stop_comp
  to wake up the the TMR handling thread, or else it will end up
  waiting forever.

- If we've a already sent an "aborted" status for a command in
  transport_check_aborted_status() then we should bail out of
  transport_send_task_abort() to avoid freeing the command twice.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@risingtidesystems.com>