void silc_socket_set_heartbeat(SilcSocketConnection sock,
                                   SilcUInt32 heartbeat,
                                   void *hb_context,
                                   SilcSocketConnectionHBCb hb_callback,
                                   SilcSchedule schedule);

    Sets the heartbeat timeout and prepares the socket for performing
    heartbeat in `heartbeat' intervals (seconds). The `hb_context' is
    allocated by the application and will be sent as argument to the
    `hb_callback' function that is called when the `heartbeat' timeout
    expires.  The callback `hb_context' won't be touched by the library
    but and must be freed by the application.  The `schedule' is the
    application's scheduler.