RDMA/core: Fix return code when modify_port isn't supported

Improve return code from ib_modify_port() by doing the following:
 - Use "-EOPNOTSUPP" instead "-ENOSYS" which is the proper return code

 - Allow only fake IB_PORT_CM_SUP manipulation for RoCE providers that
   didn't implement the modify_port callback, otherwise return
   "-EOPNOTSUPP"

Fixes: 61e0962d ("IB: Avoid ib_modify_port() failure for RoCE devices")
Link: https://lore.kernel.org/r/20191028155931.1114-2-kamalheib1@gmail.comSigned-off-by: Kamal Heib <kamalheib1@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/device.c

@@ -2408,8 +2408,12 @@ int ib_modify_port(struct ib_device *device,
 		rc = device->ops.modify_port(device, port_num,
 					     port_modify_mask,
 					     port_modify);
+	else if (rdma_protocol_roce(device, port_num) &&
+		 ((port_modify->set_port_cap_mask & ~IB_PORT_CM_SUP) == 0 ||
+		  (port_modify->clr_port_cap_mask & ~IB_PORT_CM_SUP) == 0))
+		rc = 0;
 	else
-		rc = rdma_protocol_roce(device, port_num) ? 0 : -ENOSYS;
+		rc = -EOPNOTSUPP;
 	return rc;
 }
 EXPORT_SYMBOL(ib_modify_port);