net/mlx5: Clear LAG notifier pointer after unregister

After returning from unregister_netdevice_notifier_dev_net(), set the
notifier_call field to NULL so successive call to mlx5_lag_add() will
function as expected.

Fixes: 7907f23a ("net/mlx5: Implement RoCE LAG feature")
Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/lag.c

@@ -615,8 +615,10 @@ void mlx5_lag_remove(struct mlx5_core_dev *dev)
 			break;
 
 	if (i == MLX5_MAX_PORTS) {
-		if (ldev->nb.notifier_call)
+		if (ldev->nb.notifier_call) {
 			unregister_netdevice_notifier_net(&init_net, &ldev->nb);
+			ldev->nb.notifier_call = NULL;
+		}
 		mlx5_lag_mp_cleanup(ldev);
 		cancel_delayed_work_sync(&ldev->bond_work);
 		mlx5_lag_dev_free(ldev);