qla2xxx: terminate exchange when command is aborted by LIO

The newly introduced aborted_task TFO callback has to terminate
exchange with QLogic driver, since command is being deleted and
no status will be queued to the driver at a later point.

This patch also moves the burden of releasing one cmd refcount to
the aborted_task handler.

Changed iSCSI aborted_task logic to satisfy the above requirement.

Cc: <stable@vger.kernel.org> # v3.18+
Signed-off-by: Alexei Potashnik <alexei@purestorage.com>
Acked-by: Quinn Tran <quinn.tran@qlogic.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>