net: Add net-device param to the get offloaded stats ndo

Some drivers would need to check few internal matters for
that. To be used in downstream mlx5 commit.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>