check_holddown
time_t exceeded = check_holddown(env, anchor, env->cfg->add_holddown);
time_t exceeded = check_holddown(env, anchor, env->cfg->del_holddown);
exceeded = check_holddown(env, anchor, env->cfg->keep_missing);
time_t exceeded = check_holddown(env, anchor, env->cfg->add_holddown);
time_t exceeded = check_holddown(env, anchor, env->cfg->del_holddown);
exceeded = check_holddown(env, anchor, env->cfg->keep_missing);