RC_Channel: added set_and_save_radio_trim()

# Conflicts:
#	libraries/RC_Channel/RC_Channel.h

libraries/RC_Channel/RC_Channel.h

@@ -96,6 +96,9 @@ public:
     void       save_radio_trim() { radio_trim.save();}
 
     void       set_and_save_trim() { radio_trim.set_and_save_ifchanged(radio_in);}
+
+    // set and save trim if changed
+    void       set_and_save_radio_trim(int16_t val) { radio_trim.set_and_save_ifchanged(val);}
     
     bool min_max_configured() const;