Add selection of RF band

[anderstogern]

This is exactly what I need for my Adafruit RFM bonnet. Unfortunately I use 433MHz and although part of the rfm69radio settings, it is not possible to select the frequency at which the RFM69 radio is using.

Defaulting to 915MHz limits the use of the node.

It would be very nice, if this option was added to the node configuration.