scsi: qla2xxx: Reduce the use of terminate exchange

reduce usage of terminate exchange when command encounter
resource bottle neck.  Remote initiator view it as command
drop.

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>