[gprs] correctly calculate the length of the BSSGP PDUs
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index ac04265..03794c2 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -100,6 +100,7 @@
#define msgb_bvci(__x) OBSC_MSGB_CB(__x)->bvci
#define msgb_gmmh(__x) (__x)->l3h
#define msgb_bssgph(__x) OBSC_MSGB_CB(__x)->bssgph
+#define msgb_bssgp_len(__x) ((__x)->tail - (uint8_t *)msgb_bssgph(__x))
#define msgb_bcid(__x) OBSC_MSGB_CB(__x)->bssgp_cell_id
#define msgb_llch(__x) OBSC_MSGB_CB(__x)->llch