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_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];