rtp continuous-streaming: fix BFI in the quality-suppressed case

The check for (tch_ind->lqual_cb >= bts->min_qual_norm) in
l1sap_tch_ind() has the intent of suppressing valid-seeming
speech frame output from lower layers when the link quality is
too low; this check is particularly important for FR1 codec
where the intrinsic validity check is only a 3-bit CRC which has
1/8 probability of indicating "correct" when decoding radio noise
during DTXu silence.

However, this check is effectively defeated in the current
implementation of rtp continuous-streaming: the RTP packet being
output is the presumed-bogus speech frame from lower layers,
rather than the intended zero-length payload.  Fix this bug.

Related: OS#5975
Change-Id: Icee0f57be289a0592a0197469432a012d15f224c
---
M src/common/l1sap.c
1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 89aea58..1f173db 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -1641,10 +1641,10 @@
 			return 1;
 		}
 	} else {
-		/* Are we in rtp continuous-stream special mode? If so, send
+		/* Are we in rtp continuous-streaming special mode? If so, send
 		 * out a BFI packet as zero-length RTP payload. */
 		if (bts->rtp_nogaps_mode) {
-			send_ul_rtp_packet(lchan, fn, msg->data, msg->len);
+			send_ul_rtp_packet(lchan, fn, NULL, 0);
 		} else {
 			DEBUGPGT(DRTP, &g_time, "Skipping RTP frame with lost payload (chan_nr=0x%02x)\n",
 				 chan_nr);

