MGCP: Extend tests significantly

We're now testing a variety of different permitted and illegal
transactions of the MGW.  Still lots of bits pending, particularly
also actual RTP flows.
diff --git a/mgw/MGCP_Types.ttcn b/mgw/MGCP_Types.ttcn
index 3616ddf..7d99428 100644
--- a/mgw/MGCP_Types.ttcn
+++ b/mgw/MGCP_Types.ttcn
@@ -53,7 +53,7 @@
 		variant "END('\r\n', '([\r\n])|(\r\n)')"
 	}
 
-	type record of MgcpParameter MgcpParameterList with {
+	type set of MgcpParameter MgcpParameterList with {
 		variant "BEGIN('')"
 	};