Change option from udp_discovery to server_discovery.

gns3server/web/web_server.py

@@ -299,7 +299,7 @@ class WebServer:
         if server_config.getboolean("shell"):
             asyncio.async(self.start_shell())
 
-        if sys.platform.startswith("linux") and server_config.getboolean("udp_discovery"):
+        if sys.platform.startswith("linux") and server_config.getboolean("server_discovery"):
            # UDP discovery is only supported on Linux
            udp_server_discovery = threading.Thread(target=self._udp_server_discovery, daemon=True)
            udp_server_discovery.start()