net/mlx5e: Issue direct lookup on vxlan ports by vport representors

Remove uplink representor netdevice private structure lookup, and use
mlx5 core handle directly from representor private structure to lookup
vxlan ports.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>