QMP: Fix asynchronous events delivery

Commit f039a563f2 introduces
a regression as monitor_protocol_event() will return in
the first user Monitor it finds in the QLIST_FOREACH()
loop.

The right thing to do is to only delivery an asynchronous
event if the 'mon' is a QMP Monitor.

The aforementioned commit was an early version, if it was
applied to stable (it should) this one has to be applied
there too.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit 23fabed136)

monitor.c

@@ -368,10 +368,9 @@ void monitor_protocol_event(MonitorEvent event, QObject *data)
     }
 
     QLIST_FOREACH(mon, &mon_list, entry) {
-        if (!monitor_ctrl_mode(mon))
-            return;
-
-        monitor_json_emitter(mon, QOBJECT(qmp));
+        if (monitor_ctrl_mode(mon)) {
+            monitor_json_emitter(mon, QOBJECT(qmp));
+        }
     }
     QDECREF(qmp);
 }