Enable the stats of session by default

etc/emq.conf

@@ -242,7 +242,7 @@ mqtt.session.max_awaiting_rel = 100
 mqtt.session.await_rel_timeout = 20s
 
 ## Enable Statistics: on | off
-mqtt.session.enable_stats = off
+mqtt.session.enable_stats = on
 
 ## Expired after 1 day:
 ## w - week