GCS_MAVLink: flush parameters on reboot

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1852,6 +1852,10 @@ MAV_RESULT GCS_MAVLINK::handle_preflight_reboot(const mavlink_command_long_t &pa
     // force safety on
     hal.rcout->force_safety_on();
     hal.rcout->force_safety_no_wait();
+
+    // flush pending parameter writes
+    AP_Param::flush();
+
     hal.scheduler->delay(200);
     
     // when packet.param1 == 3 we reboot to hold in bootloader