cleanup gateway code before actually changing things in https://github.com/opnsense/core/issues/2279
cleanup gateway code before actually changing things in https://github.com/opnsense/core/issues/2279

Luckily it wasn't really possible to select a gateway group in openvpn at our end, since interfaces and gatewaygroups are really different things.
We need to unravel some of this weirdness first, so we can start reimplementing the gateway code as it is now.

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core