bts-{sysmo,oc2g,lc15}: Fix RTP of AMR SID_FIRST_P1

When we receive a SID_FIRST_P1 frame from the PHY (during AMR/HR DTXu),
we must generate a SID frame on the RTP side.

The existing code
* ignored that the Amr_SidFirstP1 PHYIF message actually contains the
  RTP payload
* manually generated the same content using osmo_amr_rtp_enc()
* forgot to prefix that with the AMR CMR+TOC
* in the end, sent a completely broken (too short) AMR SID frame over RTP

Let's fix this by simply using the 7-byte RTP payload with CMR+TOC that
the PHY is providing to us.

Change-Id: I90479efcc002d497648a71e73847af54e6208358
Related: OS#5944
---
M src/osmo-bts-lc15/tch.c
M src/osmo-bts-oc2g/tch.c
M src/osmo-bts-sysmo/tch.c
3 files changed, 29 insertions(+), 24 deletions(-)

diff --git a/src/osmo-bts-lc15/tch.c b/src/osmo-bts-lc15/tch.c
index bd84bee..f9a4e21 100644
--- a/src/osmo-bts-lc15/tch.c
+++ b/src/osmo-bts-lc15/tch.c
@@ -360,7 +360,7 @@
 {
 	GsmL1_Prim_t *l1p = msgb_l1prim(l1p_msg);
 	GsmL1_PhDataInd_t *data_ind = &l1p->u.phDataInd;
-	uint8_t *payload, payload_type, payload_len, sid_first[9] = { 0 };
+	uint8_t *payload, payload_type, payload_len;
 	struct msgb *rmsg = NULL;
 	struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)].lchan[l1sap_chan2ss(chan_nr)];
 
@@ -450,14 +450,8 @@
 		rmsg = l1_to_rtppayload_efr(payload, payload_len, lchan);
 		break;
 	case GsmL1_TchPlType_Amr:
-		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
-		break;
 	case GsmL1_TchPlType_Amr_SidFirstP1:
-		memcpy(sid_first, payload, payload_len);
-		int len = osmo_amr_rtp_enc(sid_first, 0, AMR_SID, AMR_GOOD);
-		if (len < 0)
-			return 0;
-		rmsg = l1_to_rtppayload_amr(sid_first, len, lchan);
+		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
 		break;
 	}
 
diff --git a/src/osmo-bts-oc2g/tch.c b/src/osmo-bts-oc2g/tch.c
index d469740..bd97959 100644
--- a/src/osmo-bts-oc2g/tch.c
+++ b/src/osmo-bts-oc2g/tch.c
@@ -360,7 +360,7 @@
 {
 	GsmL1_Prim_t *l1p = msgb_l1prim(l1p_msg);
 	GsmL1_PhDataInd_t *data_ind = &l1p->u.phDataInd;
-	uint8_t *payload, payload_type, payload_len, sid_first[9] = { 0 };
+	uint8_t *payload, payload_type, payload_len;
 	struct msgb *rmsg = NULL;
 	struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)].lchan[l1sap_chan2ss(chan_nr)];
 
@@ -460,14 +460,8 @@
 		rmsg = l1_to_rtppayload_efr(payload, payload_len, lchan);
 		break;
 	case GsmL1_TchPlType_Amr:
-		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
-		break;
 	case GsmL1_TchPlType_Amr_SidFirstP1:
-		memcpy(sid_first, payload, payload_len);
-		int len = osmo_amr_rtp_enc(sid_first, 0, AMR_SID, AMR_GOOD);
-		if (len < 0)
-			return 0;
-		rmsg = l1_to_rtppayload_amr(sid_first, len, lchan);
+		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
 		break;
 	}
 
diff --git a/src/osmo-bts-sysmo/tch.c b/src/osmo-bts-sysmo/tch.c
index b308a5f..e901d47 100644
--- a/src/osmo-bts-sysmo/tch.c
+++ b/src/osmo-bts-sysmo/tch.c
@@ -505,7 +505,7 @@
 {
 	GsmL1_Prim_t *l1p = msgb_l1prim(l1p_msg);
 	GsmL1_PhDataInd_t *data_ind = &l1p->u.phDataInd;
-	uint8_t *payload, payload_type, payload_len, sid_first[9] = { 0 };
+	uint8_t *payload, payload_type, payload_len;
 	struct msgb *rmsg = NULL;
 	struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)].lchan[l1sap_chan2ss(chan_nr)];
 
@@ -602,14 +602,8 @@
 		break;
 #endif
 	case GsmL1_TchPlType_Amr:
-		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
-		break;
 	case GsmL1_TchPlType_Amr_SidFirstP1:
-		memcpy(sid_first, payload, payload_len);
-		int len = osmo_amr_rtp_enc(sid_first, 0, AMR_SID, AMR_GOOD);
-		if (len < 0)
-			return 0;
-		rmsg = l1_to_rtppayload_amr(sid_first, len, lchan);
+		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
 		break;
 	/* FIXME: what about GsmL1_TchPlType_Amr_SidBad? not well documented. */
 	}

