De-Activate features by default with RPi

Since RPi behaves more like a PC than Arduino, users should be able to
execute various programs without powering down the radio module, where
an Arduino needs to be re-programmed between code changes, so a full
power-down is not such a dramatic step.

Thanks to sej7278 (GitHub) see:
https://github.com/TMRh20/RF24Network/issues/2