target: use ->exectute_task for all CDB emulation

Instead of calling into transport_emulate_control_cdb from
__transport_execute_tasks for some CDBs always set up ->exectute_tasks
in the command sequence and use it uniformly.

(nab: Add default passthrough break for SERVICE_ACTION_IN)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>