net/mlx5e: Add ndo_udp_tunnel_add to VF representors

By implementing this ndo, the host stack will set the vxlan udp port
also to VF representor netdevices. This will allow the TC offload code
in the driver when it gets a tunnel key set action to identify the UDP
port as vxlan, and hence the rule will be a candidate for offloading.

Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>