RDMA/qedr: Fix NULL pointer dereference when running over iWARP without RDMA-CM

Some RoCE specific code in qedr_modify_qp was run over an iWARP device
when running perftest benchmarks without the -R option.

The commit 3e44e0ee0893 ("IB/providers: Avoid null netdev check for RoCE")
exposed this. Dropping the check for NULL pointer on ndev in
qedr_modify_qp lead to a null pointer dereference when running over
iWARP. Before the code would identify ndev as being NULL and return an
error.

Fixes: 3e44e0ee0893 ("IB/providers: Avoid null netdev check for RoCE")
Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: Michal Kalderon <Michal.Kalderon@cavium.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/qedr/verbs.c

@@ -1957,6 +1957,9 @@ int qedr_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr,
 	}
 
 	if (attr_mask & (IB_QP_AV | IB_QP_PATH_MTU)) {
+		if (rdma_protocol_iwarp(&dev->ibdev, 1))
+			return -EINVAL;
+
 		if (attr_mask & IB_QP_PATH_MTU) {
 			if (attr->path_mtu < IB_MTU_256 ||
 			    attr->path_mtu > IB_MTU_4096) {