Disable the rate_limit of MQTT/TCP listener by default.

etc/emqx.conf

@@ -766,7 +766,7 @@ listener.tcp.external.zone = external
 ##
 ## Value: rate,burst
 ## Unit: Bps
-listener.tcp.external.rate_limit = 1024,4096
+## listener.tcp.external.rate_limit = 1024,4096
 
 ## The access control rules for the MQTT/TCP listener.
 ##