core: replaced calls to client.xmlstream.send by client.send which is the right method to use. client.xmlstream should not be used directly

src/plugins/plugin_xep_0249.py

@@ -119,7 +119,7 @@ class XEP_0249(object):
                 log.warning(u"Ignoring invalid invite option: {}".format(key))
                 continue
             x_elt[key] = value
-        client.xmlstream.send(message)
+        client.send(message)
 
     def _accept(self, room_jid, profile_key=C.PROF_KEY_NONE):
         """Accept the invitation to join a MUC.