RDMA/uverbs: Fix the check for port number

The port number is only valid if IB_QP_PORT is set in the mask.
So only check port number if it is valid to prevent modify_qp from
failing due to an invalid port number.

Fixes: 5ecce4c("Check port number supplied by user verbs cmds")
Cc: <stable@vger.kernel.org> # v2.6.14+
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Tested-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/uverbs_cmd.c

@@ -1933,7 +1933,8 @@ static int modify_qp(struct ib_uverbs_file *file,
 		goto out;
 	}
 
-	if (!rdma_is_port_valid(qp->device, cmd->base.port_num)) {
+	if ((cmd->base.attr_mask & IB_QP_PORT) &&
+	    !rdma_is_port_valid(qp->device, cmd->base.port_num)) {
 		ret = -EINVAL;
 		goto release_qp;
 	}