Clear spectrum FIFO when streaming is stopped.

firmware/baseband/spectrum_collector.cpp

@@ -37,6 +37,7 @@ void SpectrumCollector::start() {
 
 void SpectrumCollector::stop() {
 	streaming = false;
+	fifo.reset_in();
 }
 
 void SpectrumCollector::set_decimation_factor(

firmware/common/fifo.hpp

@@ -42,6 +42,10 @@ public:
 		_in = _out = 0;
 	}
 
+	void reset_in() {
+		_in = _out;
+	}
+	
 	void reset_out() {
 		_out = _in;
 	}