BSSGP_Emulation: Allow a "CreateCb" to handle unknown inbound TLLI

The existing BSSGP Code assumed that the TLLIs were always known "a
priori" by the test case.  With the newly-introduced create_cb,
the user can provide a function to handle any incoming messages for an
unknown TLLL.  The default handler behaves like before: fail +
terminate.

Change-Id: Ice0e145f5a6518ff79547dd851042b7965f38e00
diff --git a/fr-net/FRNET_Tests.ttcn b/fr-net/FRNET_Tests.ttcn
index 721dd32..87b9bd7 100644
--- a/fr-net/FRNET_Tests.ttcn
+++ b/fr-net/FRNET_Tests.ttcn
@@ -65,7 +65,8 @@
 			},
 			cell_id := base + 600 + idx
 		},
-		depth := BSSGP_DECODE_DEPTH_LLC
+		depth := BSSGP_DECODE_DEPTH_LLC,
+		create_cb := refers(BSSGP_Emulation.DefaultCreateCallback)
 	};
 	return bvc;
 }