foris-controller-openvpn_client-module: Guest network & OpenVPN integration

Whenever we have OpenVPN active and that OpenVPN pushes a default route, Guest network is broken as people on Guest network can't enter VPN, obviously. Unfortunately, nowadays many people use VPN to "hide" their traffic. Not knowing what the VPN is for, I would argue that if VPN is pushing default route, it is not private network, but ISP, so guests should be allowed in. And this way, we don't break guest network setup.

Alternative would be policy based routing and push guest directly through wan even though LAN goes through VPN. Patches for that and switch between two behaviours is welcome. Personally I would actually send guest network through VPN and keep my LAN traffic going out through my ISP to avoid problems and abuse reports caused by my guests.

Depends on build!634 (merged) and solves #805