fix: add route attrs only for none-sys msgs

apps/emqx/src/emqx_broker.erl

@@ -352,7 +352,10 @@ route(Routes, Delivery = #delivery{message = Msg}, PersistRes) ->
         Delivery,
         TraceRouteAttrs,
         fun(DeliveryWithTrace) ->
-            add_route_attrs(Msg),
+            add_route_attrs(
+                (not emqx_message:is_sys(Msg)) andalso
+                    emqx_external_trace:msg_attrs(Msg)
+            ),
             do_route(Routes, DeliveryWithTrace, PersistRes)
         end
     ).
@@ -367,10 +370,13 @@ route_result({TF, Group}) ->
 do_route([], #delivery{message = Msg}, _PersistRes = []) ->
     ok = emqx_hooks:run('message.dropped', [Msg, #{node => node()}, no_subscribers]),
     ok = inc_dropped_cnt(Msg),
-    ?ext_trace_add_attrs(#{
-        'route.dropped.node' => node(),
-        'route.dropped.reason' => no_subscribers
-    }),
+    add_route_attrs(
+        (not emqx_message:is_sys(Msg)) andalso
+            #{
+                'route.dropped.node' => node(),
+                'route.dropped.reason' => no_subscribers
+            }
+    ),
     [];
 do_route([], _Delivery, PersistRes = [_ | _]) ->
     PersistRes;
@@ -490,15 +496,10 @@ inc_dropped_cnt(Msg) ->
     end.
 
 -compile({inline, [add_route_attrs/1]}).
-add_route_attrs(Msg) ->
-    %% TODO? : maybe a switch for sys messages
-    case emqx_message:is_sys(Msg) of
-        true ->
-            ok;
-        false ->
-            ?ext_trace_add_attrs(emqx_external_trace:msg_attrs(Msg)),
-            ok
-    end.
+add_route_attrs(false) ->
+    ok;
+add_route_attrs(Attrs) ->
+    ?ext_trace_add_attrs(Attrs).
 
 -compile({inline, [subscribers/1]}).
 -spec subscribers(