[feature] Add the possibility to create multiple vxlan tunnels under the same Wireguard vpn

[marino-mrc]

Hello,
It would be great to have the possibility to create multiple vxlan tunnels (with different VNIs) under the same Wireguard server.

Also, this can impact the ansible-wireguard-openwisp project but it's pretty easy to add support for this feature there.

Thanks,
Marco