Only save the changed parts of config to disk.

src/main.cpp

@@ -324,7 +324,7 @@ void setup()
         DEBUG_MSG("GPS FactoryReset requested\n");
         if (gps->factoryReset()) { // If we don't succeed try again next time
             devicestate.did_gps_reset = true;
-            nodeDB.saveToDisk();
+            nodeDB.saveToDisk(SEGMENT_DEVICESTATE);
         }
     }