Allow backup to complete on old FW versions (#268)

* Allow backup to complete on old FW versions

* Fix unit test

Author: puddly

tests/test_network_state.py

@@ -234,7 +234,7 @@ async def write_parameter(param, *args):
                     command=None,
                 )
             },
-            {"network_key.tx_counter": 0},
+            {"network_key.tx_counter": 1073741824},
             {},
         ),
         (

zigpy_deconz/zigbee/application.py

@@ -365,6 +365,11 @@ async def load_network_info(self, *, load_devices=False):
             )
         except zigpy_deconz.exception.CommandError as ex:
             assert ex.status == Status.UNSUPPORTED
+            LOGGER.debug(
+                "Conbee firmware is too old and does not support reading the frame"
+                " counter, picking a large value instead"
+            )
+            network_info.network_key.tx_counter = 2**30
 
         network_info.tc_link_key = zigpy.state.Key()
         network_info.tc_link_key.partner_ieee = await self._api.read_parameter(