ip_tun_rx_dst
tun_dst = ip_tun_rx_dst(skb, flags,
tun_dst = ip_tun_rx_dst(skb, flags, tun_id, 0);
tun_dst = ip_tun_rx_dst(skb, flags, 0, 0);
tun_dst = ip_tun_rx_dst(skb, flags, tunnel_id, md_size);