Rover: allow GCS to turn safety switch on/off

APMrover2/GCS_Mavlink.pde

@@ -927,6 +927,19 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
                 break;
             }
 
+            // set the safety switch position
+            if (packet.base_mode & MAV_MODE_FLAG_DECODE_POSITION_SAFETY) {
+                if (packet.custom_mode == 0) {
+                    // turn safety off (pwm outputs flow to the motors)
+                    hal.rcout->force_safety_off();
+                } else if (packet.custom_mode == 1) {
+                    // turn safety on (no pwm outputs to the motors)
+                    hal.rcout->force_safety_on();
+                }
+                break;
+            }
+
+            // check if we are setting the control mode
             if (!(packet.base_mode & MAV_MODE_FLAG_CUSTOM_MODE_ENABLED)) {
                 // we ignore base_mode as there is no sane way to map
                 // from that bitmap to a APM flight mode. We rely on