GCS_MAVLink: allow control to be return to radio for higher-numbered RC_CHANNELS_OVERRIDE

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -3136,7 +3136,10 @@ void GCS_MAVLINK::handle_rc_channels_override(const mavlink_message_t &msg)
         // Per MAVLink spec a value of zero or UINT16_MAX means to
         // ignore this field.
         if (override_data[i] != 0 && override_data[i] != UINT16_MAX) {
-            RC_Channels::set_override(i, override_data[i], tnow);
+            // per the mavlink spec, a value of UINT16_MAX-1 means
+            // return the field to RC radio values:
+            const uint16_t value = override_data[i] == (UINT16_MAX-1) ? 0 : override_data[i];
+            RC_Channels::set_override(i, value, tnow);
         }
     }
 }