MT#55283 fix DTMF send scheduling

Don't try to interpret or schedule DTMF packets if we're just doing RTP
passthrough.

Without tracking the seqencing and timestamping of the primary media
stream, we cannot actually schedule DTMF packets properly. Use the
presence of a defined output sequence number to make this determination.

The other case that uses a predefined output sequence number is when
media is coming from a pre-coded media player stream. The same thing
applies: These packets are already scheduled, so we can skip trying to
schedule them again.

closes #1638

Change-Id: I2d2c20e731f20a3136ca3eee37f0b521062cdb11

daemon/codec.c

@@ -1941,6 +1941,16 @@ void codec_output_rtp(struct media_packet *mp, struct codec_scheduler *csch,
 	ssrc_ctx_hold(ssrc_out);
 	p->ssrc_out = ssrc_out;
 
+	long long ts_diff_us = 0;
+
+	// ignore scheduling if a sequence number was supplied. in that case we're just doing
+	// passthrough forwarding (or are handling some other prepared RTP stream) and want
+	// to send the packet out immediately.
+	if (seq != -1) {
+		p->ttq_entry.when = rtpe_now;
+		goto send;
+	}
+
 	// this packet is dynamically allocated, so we're able to schedule it.
 	// determine scheduled time to send
 	if (csch->first_send.tv_sec && handler->dest_pt.clock_rate) {
@@ -1962,8 +1972,7 @@ void codec_output_rtp(struct media_packet *mp, struct codec_scheduler *csch,
 		csch->first_send_ts = ts;
 	}
 
-	long long ts_diff_us
-		= timeval_diff(&p->ttq_entry.when, &rtpe_now);
+	ts_diff_us = timeval_diff(&p->ttq_entry.when, &rtpe_now);
 
 	csch->output_skew = csch->output_skew * 15 / 16 + ts_diff_us / 16;
 	if (csch->output_skew > 50000 && ts_diff_us > 10000) { // arbitrary value, 50 ms, 10 ms shift
@@ -1986,6 +1995,7 @@ void codec_output_rtp(struct media_packet *mp, struct codec_scheduler *csch,
 		ts_diff_us = timeval_diff(&p->ttq_entry.when, &rtpe_now); // should be 0 now
 	}
 
+send:
 	ilogs(transcoding, LOG_DEBUG, "Scheduling to send RTP packet (seq %u TS %lu) in %s%lli.%01lli ms (at %lu.%06lu)",
 			ntohs(rh->seq_num),
 			ts,