sccp: Call a function on UDT messages

Allow to handle UDT messages by subclassing and reimplementing,
by default only log the UDT.

SCCPHandler.st

@@ -328,9 +328,18 @@ Object subclass: SCCPHandler [
             ^ true
         ].
 
+        (sccp isKindOf: Osmo.SCCPUDT) ifTrue: [
+            self handleUDT: sccp.
+            ^ true
+        ].
+
         self dispatchMessage: sccp.
     ]
 
+    handleUDT: aSCCP [
+        self logNotice: 'Incomind UDT message' area: #sccp.
+    ]
+
 
     connection: aConnection [
         connection := aConnection.