IB/qib: Precompute timeout jiffies to optimize latency

A new field is added to qib_qp called timeout_jiffies. It is
initialized upon create and modify.

The field is now used instead of a computation based on qp->timeout.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib_verbs.h

@@ -496,6 +496,7 @@ struct qib_qp {
 	u32 s_last;             /* last completed entry */
 	u32 s_ssn;              /* SSN of tail entry */
 	u32 s_lsn;              /* limit sequence number (credit) */
+	unsigned long timeout_jiffies;  /* computed from timeout */
 	struct qib_swqe *s_wq;  /* send work queue */
 	struct qib_swqe *s_wqe;
 	struct qib_rq r_rq;             /* receive work queue */