Copter: reduce SONAR_GAIN to 0.8 (was 2.0)

ArduCopter/config.h

@@ -277,7 +277,7 @@
 #endif
 
 #ifndef SONAR_GAIN_DEFAULT
- # define SONAR_GAIN_DEFAULT 2.0            // gain for controlling how quickly sonar range adjusts target altitude (lower means slower reaction)
+ # define SONAR_GAIN_DEFAULT 0.8            // gain for controlling how quickly sonar range adjusts target altitude (lower means slower reaction)
 #endif
 
 #ifndef THR_SURFACE_TRACKING_VELZ_MAX