Make MdeModulePkg GCC clean.

It also pass ICC+IPF and MYTOOLS+EBC build.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@3711 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Dispatcher.c

@@ -681,6 +681,8 @@ Tcp4Dispatcher (
 
     return Tcp4Route (Tcb, (TCP4_ROUTE_INFO *) Data);
 
+  default:
+    return EFI_UNSUPPORTED;
   }
 
   return EFI_SUCCESS;