net/mlx5: E-Switch, Introduce get vf statistics

Add support to get VF statistics using query vport
counter command.

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