net/mlx5_core: Introduce flow steering destination of type counter

When adding a flow steering rule with a counter, need to supply a
destination of type MLX5_FLOW_DESTINATION_TYPE_COUNTER, with a pointer
to a struct mlx5_fc.
Also, MLX5_FLOW_CONTEXT_ACTION_COUNT bit should be set in the action.

Signed-off-by: Amir Vadai <amirva@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>