SDAP: Do not set is_offline if ignore_mark_offline is set
    
    Required for:
    https://fedorahosted.org/sssd/ticket/2637
    
    The caller of the sdap_id_op requests can set the ignore_mark_offline
    flag to avoid the sdap_id_op from marking the whole back end as offline.
    
    However, there was a small bug - the is_offline internal sdap_id_op flag
    was still being set. As a consequence, the error code from the
    connection was ignored and EAGAIN was always returned.
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>