AP_UAVCAN: refuse to reboot via CAN if armed

libraries/AP_UAVCAN/AP_UAVCAN_Servers.cpp

@@ -88,6 +88,10 @@ class AP_UAVCAN_RestartRequestHandler : public uavcan::IRestartRequestHandler {
 public:
     bool handleRestartRequest(uavcan::NodeID request_source) override {
         // swiped from reboot handling in GCS_Common.cpp
+        if (hal.util->get_soft_armed()) {
+            // refuse reboot when armed
+            return false;
+        }
         AP_Notify *notify = AP_Notify::get_singleton();
         if (notify) {
             AP_Notify::flags.firmware_update = 1;