Update api.py

Hopefully gracefully shut down for the socket servers

Author: HAEdwin

custom_components/apsystems_ecu_proxy/api.py

@@ -81,6 +81,7 @@ async def stop(self):
         if self.server:
             self.server.close()
             await self.server.wait_closed()
+            self.server = None
             _LOGGER.debug("Server for port %s stopped", self.port)
 
     async def data_received(