mqtt: handle connection shutdown

`{shutdown, Reason}` must be handled into handle_call and not handle_info
`rabbitmqctl close_all_user_connections` calls rabbit_reader which does
a call into the process, the same as rabbitmq_management

Author: dcorbacho

deps/rabbitmq_mqtt/src/rabbit_mqtt_reader.erl

@@ -109,6 +109,11 @@ init(Ref) ->
 handle_call({info, InfoItems}, _From, State) ->
     {reply, infos(InfoItems, State), State, ?HIBERNATE_AFTER};
 
+handle_call({shutdown, Explanation} = Reason, _From, State = #state{conn_name = ConnName}) ->
+    %% rabbit_networking:close_all_user_connections -> rabbit_reader:shutdow
+    ?LOG_INFO("MQTT closing connection ~tp: ~p", [ConnName, Explanation]),
+    {stop, Reason, ok, State};
+
 handle_call(Msg, From, State) ->
     {stop, {mqtt_unexpected_call, Msg, From}, State}.