Onboarding: add support for non-AP IP addresses

[m-roberts]

An easy way to do this would be to cycle through all available IP addresses on the browser page. However, this lacks clarity of which IP address is preferred.

Another option might be for SELECT to alternate the IP address shown, but this is also somewhat problematic as there's no cue to do that. This might be remedied with a brief explanation somewhere, but this then risks unnecessary additional pages.

We could also prefer non-local IP addresses (i.e. look at eth0 and wlan0), but this would cause confusion given the fact that it's after the connection guide which is specifically aimed at AP mode.

We could just extend the menu's build information, but this is already not very clearly presented - though that itself could be solved with a change in interface (such as cycling through menu options with SELECT/CANCEL only).