RESPONDERS: Fix terminating idle connections
    
    The client_idle_handler() function tried to schedule another tevent
    timer to check for idle client connections in case the current
    connection was still valid, but in doing so, it also stored the current
    time into the last_request_time field of the client context.
    
    This kept the connection always alive, because the last_request_time
    could then never be older than the timeout.
    
    This patch changes the setup_client_idle_timer() function to only do
    what the synopsis says and set the idle timer. The caller (usually the
    function that accepts the connection) is supposed to store the request
    time itself.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3448
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>