PWM RSSI output

This is a huge kludge. It was written in a rush for very crude automatic direction finding.

When enabled, the demodulated audio output is replaced by a rectangular wave tone of either 800Hz in NFM mode or 500Hz in WFM mode. The wave's duty cycle is the RSSI.

The data path is very messy: the RSSI thread running on the baseband core sends groups of values to the application's RSSI widget, it computes the average value and sends it back to the baseband module which generates the audio output.