gmm: Ciphering Key Sequence Number IE has half octet tag

As per 3GPP TS 24.008:
* 10.5.1.2 Ciphering Key Sequence Number
* Table 9.4.9/TS 24.00

The IE is so far being encoded manually, hence why it worked fine until
now.

Change-Id: Ic220113f30377a14cbe3550a04cd04f3caef49cf
---
M src/sgsn/gprs_gmm.c
1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/sgsn/gprs_gmm.c b/src/sgsn/gprs_gmm.c
index 5bf66c3..547edbb 100644
--- a/src/sgsn/gprs_gmm.c
+++ b/src/sgsn/gprs_gmm.c
@@ -70,7 +70,7 @@
 
 static const struct tlv_definition gsm48_gmm_att_tlvdef = {
 	.def = {
-		[GSM48_IE_GMM_CIPH_CKSN]	= { TLV_TYPE_FIXED, 1 },
+		[GSM48_IE_GMM_CIPH_CKSN]	= { TLV_TYPE_SINGLE_TV, 1 },
 		[GSM48_IE_GMM_TIMER_READY]	= { TLV_TYPE_TV, 1 },
 		[GSM48_IE_GMM_ALLOC_PTMSI]	= { TLV_TYPE_TLV, 0 },
 		[GSM48_IE_GMM_PTMSI_SIG]	= { TLV_TYPE_FIXED, 3 },

