I don’t know how you want to use the GL-AR150 exactly, but if you use it as an extra hotspot in your house isn’t it more practical to configure the GL-AR150 as a accesspoint instead of a router?
*Jeroen still needs to figure that out himself. :-PThere is enough OpenWRT documentation how to configure OpenWRT for being an accesspoint instead of a router. eth0 then will become just LAN eth0 instead of WAN and eth1 will stay LAN eth1.