RC: set dead zone only if parameter has not been set by user

libraries/RC_Channel/RC_Channel.cpp

@@ -95,9 +95,11 @@ RC_Channel::set_angle(int16_t angle)
 }
 
 void
-RC_Channel::set_dead_zone(int16_t dzone)
+RC_Channel::set_default_dead_zone(int16_t dzone)
 {
-    _dead_zone.set_and_save(abs(dzone >>1));
+    if (!_dead_zone.load()) {
+        _dead_zone.set(abs(dzone));
+    }
 }
 
 void

libraries/RC_Channel/RC_Channel.h

@@ -49,7 +49,7 @@ public:
     void        set_angle(int16_t angle);
     void        set_reverse(bool reverse);
     bool        get_reverse(void);
-    void        set_dead_zone(int16_t dzone);
+    void        set_default_dead_zone(int16_t dzone);
 
     // read input from APM_RC - create a control_in value
     void        set_pwm(int16_t pwm);