[fix] Corrected initial field value assignment in AbstractDevice class

Author: pandafy

openwisp_controller/config/base/device.py

@@ -339,7 +339,7 @@ def _get_initial_values_for_checked_fields(self):
             return
         self.refresh_from_db(fields=present_values.keys())
         for field in self._changed_checked_fields:
-            setattr(self, f"_initial_{field}", field)
+            setattr(self, f"_initial_{field}", getattr(self, field))
             setattr(self, field, present_values[field])
 
     def _check_name_changed(self):