KiwiSDR: variable sample rate

[f4exb]

Following this post on the Group it appears that some servers use a 20 kS/s sample rate (20250 S/s actually) instead of the fixed 12 kS/s. For now the KiwiSDR plugin assumes always a 12 kS/s rate.

It is possible to get the actual rate by analyzing the value here instead of trying to find the 12000 value. In fact if anything is different the code in the if block is not executed and eventually connection is closed.

A debug message added in this place will show that the actual rate is sent from the server:
2022-11-26 11:29:00.490 (D) KiwiSDRWorker::onBinaryMessageReceived: audio_rate=20250