Add fine adjustment to the DMR/YSF thresholds.

YSFRX.h

@@ -35,6 +35,8 @@ public:
 
   void reset();
 
+  void setThreshold(int8_t threshold);
+
 private:
   uint32_t    m_pll;
   bool        m_prev;
@@ -49,6 +51,7 @@ private:
   uint16_t    m_lostCount;
   q15_t       m_centre;
   q15_t       m_threshold;
+  q15_t       m_scale;
 
   void processNone(q15_t sample);
   void processData(q15_t sample);