Optionally allow 3B+ to be connected via Ethernet [Jamming protection]

[jkaczman]

Given the Raspberry Pi 3B+ has an Ethernet port, we could support both WiFi and Ethernet connectivity from it. Some people may wish to opt for Ethernet to protect against WiFi jamming.

It would be simple to add: a step within pairing, that if it's a 3B+ and has connectivity already, skip asking the user for WiFi credentials.

Probably best to do this after the pairing refactor is merged and 3B+ support is added.

[arrdalan]

Raspberry Pi 3B+ can support PoE/PoE+ too:

https://www.raspberrypi.com/products/poe-hat/
https://www.raspberrypi.com/products/poe-plus-hat/