mpegts: When playing mpegts over rtp/rtsp/sdp, lavf must still read PAT/SDT to get available streams

The code path using for mpegts over rtp doesn't open the demuxer using
mpegts_read_header,
so it never starts listening for PAT/SDT, only uses auto_guess

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mpegts.c

@@ -1871,6 +1871,9 @@ MpegTSContext *ff_mpegts_parse_open(AVFormatContext *s)
     ts->raw_packet_size = TS_PACKET_SIZE;
     ts->stream = s;
     ts->auto_guess = 1;
+    mpegts_open_section_filter(ts, SDT_PID, sdt_cb, ts, 1);
+    mpegts_open_section_filter(ts, PAT_PID, pat_cb, ts, 1);
+
     return ts;
 }