BSSMAP_Emulation: Decode DTAP

It's quite cumbersome if the user of the BSSMAP_Emulation (the ConnHdlr)
will have to manually decode the DTAP in every BSSAP/DTAP message he
receives (and encode on the transmit side).  Let's introduce a new
optional mode in which the DTAP messages are already decoded for
more convenient matching inside the ConnHdlr.

Change-Id: I35cd4ea78aca0ce7c7d745e082d7289882c11e81
diff --git a/bsc-nat/MSC_ConnectionHandler.ttcn b/bsc-nat/MSC_ConnectionHandler.ttcn
index b038ce5..0a06759 100644
--- a/bsc-nat/MSC_ConnectionHandler.ttcn
+++ b/bsc-nat/MSC_ConnectionHandler.ttcn
@@ -56,7 +56,9 @@
 
 const BssmapOps MSC_BssmapOps := {
 	create_cb := refers(CreateCallback),
-	unitdata_cb := refers(UnitdataCallback)
+	unitdata_cb := refers(UnitdataCallback),
+	decode_dtap := false,
+	role_ms := false
 }
 
 type enumerated MSC_State {