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/pcu/SGSN_Components.ttcn b/pcu/SGSN_Components.ttcn
index 5f05595..ca1dec6 100644
--- a/pcu/SGSN_Components.ttcn
+++ b/pcu/SGSN_Components.ttcn
@@ -33,7 +33,8 @@
 					},
 					cell_id := 20960
 				},
-				depth := BSSGP_DECODE_DEPTH_BSSGP
+				depth := BSSGP_DECODE_DEPTH_BSSGP,
+				create_cb := refers(BSSGP_Emulation.DefaultCreateCallback)
 			}
 		}
 	};