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/tests/bsc-nat/bsc_nat_test.ok b/openbsc/tests/bsc-nat/bsc_nat_test.ok
index cbedc85..ab04f42 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.ok
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.ok
@@ -35,4 +35,5 @@
 IMSI: 12123127 CM: 3 LU: 5
 IMSI: 12123128 CM: 3 LU: 6
 IMSI: 12123124 CM: 3 LU: 2
+Testing LAC extraction from SCCP CR
 Testing execution completed.