fix(subprotocol): fix bad configuration item name for subprotocol

etc/emqx.conf

@@ -1580,7 +1580,7 @@ listener.ws.external.access.1 = allow all
 ## Supported subprotocols
 ##
 ## Default: mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
-## listener.ws.external.supported_protocols = mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
+## listener.ws.external.supported_subprotocols = mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
 
 ## Enable the Proxy Protocol V1/2 if the EMQ cluster is deployed behind
 ## HAProxy or Nginx.
@@ -1801,7 +1801,7 @@ listener.wss.external.access.1 = allow all
 ## Supported subprotocols
 ##
 ## Default: mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
-## listener.wss.external.supported_protocols = mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
+## listener.wss.external.supported_subprotocols = mqtt, mqtt-v3, mqtt-v3.1.1, mqtt-v5
 
 ## Enable the Proxy Protocol V1/2 support.
 ##