net/mlx5: Use available mlx5_vport struct

Several functions need to access mlx5_vport and vport_num.
When these functions are called, caller already has mlx5_vport*
available.
Hence pass such mlx5_vport pointer.

This is preparation patch to add error checks to
mlx5_eswitch_get_vport() and to return error status.
By doing so, reduce places where error check of mlx5_eswitch_get_vport()
can be avoided.

While doing such change, mlx5_eswitch_query_vport_drop_stats() gets
corrected to work on vport, instead of vport_idx.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>