qla2xxx: Remove dependency on hardware_lock to reduce lock contention.

Sessions management (add, deleted, modify) currently are serialized
through the hardware_lock.  Hardware_lock is a high traffic lock.
This lock is accessed by both the transmit & receive sides.

Sessions management is now moved off to another lock call sess_lock.
This is done to reduce lock contention and increase traffic throughput.

Signed-off-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>