Feature request: Automatic route config between ifaces

[ingve]

Feature request: Automatic route config between ifaces. E.g. not having to specify all the routes explicitly if you e.g. enable routing / forwarding on an iface
I like this idea, as long as we're explicit per iface - e.g. we don't want to be in a situation where you suddenly have routes to / from uplink unless you explicitly enabled it

(request from customer, reported by @alfred-bratterud on Slack)