RESPONDER: Removing neg_timeout from ifp repsonder
    
    Timeout of negative cache is handled by context of negative cache
    itself. This patch removes neg_timeout parameter from ifp_ctx and from
    ifp_user_get_attr_state.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2317
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>