GTP: convert from translation port to dual faced port

I spent numerous hours in trying to avoid the dual faced port from
segfaulting, but in the end didn't succeed :(

The easy way was then simply to fall back to the known-working pattern
of the dual-faced port, which I already successfully used also on the NS
module for the Gb Inteface
diff --git a/ggsn_tests/GTP_CodecPort_CtrlFunctDef.cc b/ggsn_tests/GTP_CodecPort_CtrlFunctDef.cc
index a8a014b..c0b9391 100644
--- a/ggsn_tests/GTP_CodecPort_CtrlFunctDef.cc
+++ b/ggsn_tests/GTP_CodecPort_CtrlFunctDef.cc
@@ -2,9 +2,6 @@
 #include "IPL4asp_PT.hh"
 #include "GTP_CodecPort.hh"
 
-using namespace IPL4asp__PortType;
-using namespace IPL4asp__Types;
-
 namespace GTP__CodecPort__CtrlFunct {
 
   IPL4asp__Types::Result f__IPL4__listen(
@@ -54,5 +51,16 @@
   {
     return f__IPL4__PROVIDER__getUserData(portRef, connId, userData);
   }
-  
+
+
+  IPL4asp__Types::Result f__GTPU__listen(
+    GTP__CodecPort::GTPU__PT& portRef,
+    const IPL4asp__Types::HostName& locName,
+    const IPL4asp__Types::PortNumber& locPort,
+    const IPL4asp__Types::ProtoTuple& proto,
+    const IPL4asp__Types::OptionList& options)
+  {
+    return f__IPL4__PROVIDER__listen(portRef, locName, locPort, proto, options);
+  }
+
 }