[gprs] Ensure msgb->l3h points to Layer3 (04.08)

In the old code
	l3h = BSSGP, l4h = LLC, cb[gmmh] = 04.08
Now, this has been changed to
	cb[bssgph] = BSSGP, cb[llch] = LLC, l3h = 04.08

This way, GSM general 04.08 and GPRS 04.08 code can expect a
GSM 04.08 header at msgb->l3h
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index c124fae..f011041 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -81,7 +81,8 @@
 
 /* the data structure stored in msgb->cb for openbsc apps */
 struct openbsc_msgb_cb {
-	unsigned char *gmmh;
+	unsigned char *bssgph;
+	unsigned char *llch;
 
 	u_int16_t nsei;
 	u_int16_t bvci;
@@ -90,10 +91,11 @@
 } __attribute__((packed));
 #define OBSC_MSGB_CB(__msgb)	((struct openbsc_msgb_cb *)&((__msgb)->cb[0]))
 #define msgb_tlli(__x)		OBSC_MSGB_CB(__x)->tlli
-#define msgb_gmmh(__x)		OBSC_MSGB_CB(__x)->gmmh
 #define msgb_nsei(__x)		OBSC_MSGB_CB(__x)->nsei
 #define msgb_bvci(__x)		OBSC_MSGB_CB(__x)->bvci
-#define msgb_llch(__x)		(__x)->l4h
+#define msgb_gmmh(__x)		(__x)->l3h
+#define msgb_bssgph(__x)	OBSC_MSGB_CB(__x)->bssgph
+#define msgb_llch(__x)		OBSC_MSGB_CB(__x)->llch
 
 struct msgb;
 typedef int gsm_cbfn(unsigned int hooknum,