Provide utility for sending test PoC data

[shawaj]

This is more of a feature request to help new third party manufacturers more easily get through the FCC and other certification testing.

As per the application note from DeWi the PoC is transmitting on non standard channels for LoRaWAN:
Tech Application note for FCC testing and certification of Helium Compatible Devices(1).pdf

As this is non-standard it would be useful to add some commands to provide a continuous stream of fake/emulated PoC packets across the frequency spectrum (902.3 to 914.9 MHz) indicated in the document (additionally, allowing this on any frequency plan could be useful for non-FCC purposes too).

This is then agnostic of the HAL/packet forwarder and can improve the time to market for new manufacturers.

[madninja]

That sounds like a very different utility for testing than this repo provides?