The you just need to redefine one of the LAN ports as WAN (LAN1 would make sense, as that's what AVM does in this scenario). Take it out of the (br-)lan bridge and use it as WAN, very similar to the bthub5 setup.
The you just need to redefine one of the LAN ports as WAN (LAN1 would make sense, as that's what AVM does in this scenario). Take it out of the (br-)lan bridge and use it as WAN, very similar to the bthub5 setup.