scsi: qla2xxx: Reduce holding sess_lock to prevent CPU lock-up

- Reduce sess_lock holding to prevent CPU Lock up. sess_lock was held across
  fc_port registration and deletion.  These calls can be blocked by upper
  layer. Sess_lock is also being accessed by interrupt thread.

- Reduce number of loops in processing work_list to prevent kernel complaint
  of CPU lockup or holding sess_lock.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>