SilcBool silc_schedule_set_listen_fd(SilcSchedule schedule,
                                         SilcUInt32 fd,
                                         SilcTaskEvent mask,
                                         SilcBool send_events);

    Sets a file descriptor `fd' to be listened by the scheduler for
    `mask' events.  To tell scheduler not to listen anymore for this
    file descriptor call the silc_schedule_unset_listen_fd function.
    When new task is created with silc_schedule_task_add the event
    for the task's fd is initially set to SILC_TASK_READ. If you need
    to control the task's fd's events you must call this function
    whenever you need to change the events. This can be called multiple
    times to change the events.

    If the `send_events' is TRUE then this function sends the events
    in `mask' to the application.  If FALSE then they are sent only
    after the event occurs in reality.  In normal cases the `send_events'
    is set to FALSE.

    Returns FALSE if the operation could not performed and TRUE if it
    was a success.