restore RemoveCallback3 as RemoveCallbackUsr to get (un)interest working again

callback.c

@@ -271,6 +271,36 @@ int RemoveCallback2(pICallBack self, void *pUserData)
   return 1;
 }
 
+/*--------------------------------------------------------------------------*/
+/*
+ * Remove callback in context -
+ * if the callback function matches and the user function returns zero
+ */
+int RemoveCallbackUsr(pICallBack self, SICSCallBack pFunc, int (*userfunc)(const void* pContext, const void* pUserData), void *pCtx)
+{
+  pCallBackItem pItem;
+
+  if (!CheckPointer(self))
+  {
+    return 0;
+  }
+
+  pItem = self->head;
+  while (pItem != NULL) {
+    if (pItem->pFunc == pFunc) {
+      if(userfunc(pCtx, pItem->pUserData) == 0) {
+        if (debug) {
+          printf("Killing callback at %p\n", self);
+        }
+        pItem->killFlag = 1;
+      }
+    }
+    pItem = pItem->next;
+  }
+  cleanCallbackList(self);
+  return 1;
+}
+
   /*--------------------------------------------------------------------------*/
 int RemoveCallbackCon(pICallBack self, SConnection * con)
 {