RTP: audio/MPA needs to be packetized

(see http://forum.videolan.org/viewtopic.php?f=2&t=56224&p=186350)
(cherry picked from commit 575b1c1c)

modules/demux/rtp.c

@@ -555,6 +555,7 @@ static void *mpa_init (demux_t *demux)
 
     es_format_Init (&fmt, AUDIO_ES, VLC_FOURCC ('m', 'p', 'g', 'a'));
     fmt.audio.i_channels = 2;
+    fmt.b_packetized = false;
     return codec_init (demux, &fmt);
 }