target: Make core_tmr_abort_task() skip TMFs

The loop in core_tmr_abort_task() iterates over sess_cmd_list.
That list is a list of regular commands and task management
functions (TMFs). Skip TMFs in this loop instead of letting
the target drivers filter out TMFs in their get_task_tag()
callback function.

(Drop bogus check removal in tcm_qla2xxx_get_task_tag - nab)

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: <qla2xxx-upstream@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>