IB/srp: stop sharing the host lock with SCSI

We don't need protection against the SCSI stack, so use our own lock to
allow parallel progress on separate CPUs.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
[ broken out and small cleanups by David Dillow ]
Signed-off-by: David Dillow <dillowda@ornl.gov>

drivers/infiniband/ulp/srp/ib_srp.h

@@ -144,6 +144,8 @@ struct srp_target_port {
 
 	struct srp_iu	       *rx_ring[SRP_RQ_SIZE];
 
+	spinlock_t		lock;
+
 	struct list_head	free_tx;
 	struct srp_iu	       *tx_ring[SRP_SQ_SIZE];