fbw: add optional channel number config while creating network and per-radio distance

[ggsnpdsn]

[ggsnpdsn]

When creating a network, you can choose to configure the channel number, transmission power, country, distance and other parameters, which are necessary.

[ilario]

Especially the distance parameter (that should be set on a per-antenna basis), has a very strong impact on the connection performances and thus is important for lime-app to allow the user to configure it (maybe with the "use auto if available" option also, see https://github.com/libremesh/lime-packages/issues/932).

Regarding the country, there is an issue here #291 and here https://github.com/libremesh/lime-packages/issues/699 and the backend support is already ready since https://github.com/libremesh/lime-packages/pull/843. Also the 5 GHz channels setting, like the country settings, are required for allowing the users to comply with local regulations.

Other things that would be needed are indicated here https://github.com/libremesh/lime-packages/issues/327