net/mlx5e: Disable netdev after close

Disable netdev should come after it was closed, although no harm of doing it
before -hence the MLX5E_STATE_DESTROYING bit- but it is more natural this way.

Fixes: 26e59d80 ("net/mlx5e: Implement mlx5e interface attach/detach callbacks")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>