ASCI: Add decoding of mobile identity in TALKER INDICATION

gsm48.c provides a function to decode mobile identity from various
messages. TALKER INDICATION is sent by the talking subscriber of a voice
group call to idenitfy the current talker. The mobile identity is
required to distinguish between calling subscriber and other subscribers.

Related: OS#4854
Change-Id: I331fac82e3c15abb01f554b2e70576100f2eea2d
---
M src/gsm/gsm48.c
1 file changed, 26 insertions(+), 0 deletions(-)

diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index 3ec7547..4f79026 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -955,6 +955,17 @@
 			cm2_buf = (uint8_t*)&paging_response->cm2;
 			goto got_cm2;
 
+		case GSM48_MT_RR_TALKER_IND:
+			/* Check minimum size: Header + CM2 LV + minimum MI LV */
+			if (l3_len < sizeof(*gh) + 4 + 2)
+				return -EBADMSG;
+			/* CM2 shall be always 3 bytes in length */
+			if (gh->data[0] != 3)
+				return -EBADMSG;
+			cm2_len = gh->data[0];
+			cm2_buf = gh->data + 1;
+			goto got_cm2;
+
 		default:
 			break;
 		}

