nat: Extract the LAC/CI from the Complete Layer3 Information

Find the Cell Identifier from the Complete Layer3 Information and
store it for future reference. We could begin to verify that the
LAC/CI used really belongs to the BSC.
diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index c5234d4..1393945 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -502,4 +502,7 @@
 void bsc_nat_ctrl_del_pending(struct bsc_cmd_list *pending);
 int bsc_nat_handle_ctrlif_msg(struct bsc_connection *bsc, struct msgb *msg);
 
+int bsc_nat_extract_lac(struct bsc_connection *bsc, struct nat_sccp_connection *con,
+				struct bsc_nat_parsed *parsed, struct msgb *msg);
+
 #endif
diff --git a/openbsc/include/openbsc/bsc_nat_sccp.h b/openbsc/include/openbsc/bsc_nat_sccp.h
index a21684b..34aa632 100644
--- a/openbsc/include/openbsc/bsc_nat_sccp.h
+++ b/openbsc/include/openbsc/bsc_nat_sccp.h
@@ -80,6 +80,9 @@
 	int imsi_checked;
 	char *imsi;
 
+	uint16_t lac;
+	uint16_t ci;
+
 	/* remember which Transactions we run over the bypass */
 	char ussd_ti[8];