unmarshal_u32
if ((n = unmarshal_u32(b)) == 0) {
p->max_refresh_time = unmarshal_u32(b);
p->min_refresh_time = unmarshal_u32(b);
p->max_retry_time = unmarshal_u32(b);
p->min_retry_time = unmarshal_u32(b);
p->min_expire_time = unmarshal_u32(b);
p->ixfr_number = unmarshal_u32(b);
p->verifier_timeout = unmarshal_u32(b);