When both the pfn and pUser parameters are NULL, all registered callbacks are cancelled.
- pISocket:Pointer to the ISocket Interface for which the callback function needs to be de-registered.
- pfn:Pointer to the callback function that needs to be cancelled.
- pUser:Callback data that was used to register the callback.
void ISOCKET_Cancel(ISocket * pISocket, PFNNOTIFY pfn, void * pUser)