Add decode percentage for indication of signal quality

[markdconner]

For the LMS-6 sondes at least, there is a serial number for each telemetry report. To get a heads-up of a weakening signal, the percentage of the reports decoded in the last 30 or 60 seconds would be an indicator it's time to start adjusting the antenna.

[darksidelemm]

TBH that's kind of what the SNR indication is meant to do. However, that doesn't work for 1680 MHz sondes because the signal has such a huge modulation index that the fsk_demod I use doesn't work well (I do need to re-test this with the latest fsk_demod update, but i'm not hopeful).

We also currently don't send ever received position from auto_rx into chasemapper (default is an update every 5 seconds). This behaviour could probably be changed without any significant performance impact, so what you propose could probably be made possible

[markdconner]

It looked like the other sondes might have more "toys" available for such things. This would be something of a kludge to do something similar for the 1680's, but perhaps a helpful one.