net/mlx5e: Use ndo_stop explicitly at shutdown flow

The current implementation copies the flow of ndo_stop instead of
calling it explicitly, Fixed it.

Fixes: 5fc7197d

 ("net/mlx5: Add pci shutdown callback")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>