802.11s - Simple VXLAN trunk

This is still WIP, this can be achieved in a same way vxlan-vlan is done but just instead setting the only created VXLAN as a VLAN port, just create more VXLANs with different VNIs and the same remote address. Given no VLANs will be MTU can be set to 1570.

I still haven't tested this myself so I prefer to do it before adding specific configuration settings.

I have done some preliminary tests and it works, just as bridges are needed per subnet, if a particular bridge has no physical port assigned the option to bring up the bridge empty must be enabled.