qmp: Revert change to handle_qmp_command tracepoint

Commit 71da4667 "monitor: separate QMP parser and dispatcher" moved
the handle_qmp_command tracepoint from handle_qmp_command() to
monitor_qmp_dispatch_one().  This delays tracing from enqueue time to
dequeue time.  Revert that.  Dequeue remains adequately visible via
tracepoint monitor_qmp_cmd_in_band.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <20180703085358.13941-14-armbru@redhat.com>

monitor.c

@@ -4184,12 +4184,6 @@ static void monitor_qmp_dispatch_one(QMPRequest *req_obj)
 
     g_free(req_obj);
 
-    if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
-        QString *req_json = qobject_to_json(req);
-        trace_handle_qmp_command(mon, qstring_get_str(req_json));
-        qobject_unref(req_json);
-    }
-
     old_mon = cur_mon;
     cur_mon = mon;
 
@@ -4283,6 +4277,12 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
         qdict_del(qdict, "id");
     } /* else will fail qmp_dispatch() */
 
+    if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
+        QString *req_json = qobject_to_json(req);
+        trace_handle_qmp_command(mon, qstring_get_str(req_json));
+        qobject_unref(req_json);
+    }
+
     /* Check against the request in general layout */
     qdict = qmp_dispatch_check_obj(req, qmp_oob_enabled(mon), &err);
     if (!qdict) {