INGRESS_FWDNS_MAGIC
if (skb->tstamp == INGRESS_FWDNS_MAGIC)
skb->tstamp = INGRESS_FWDNS_MAGIC;
if (bpf_skb_set_tstamp(skb, INGRESS_FWDNS_MAGIC,
skb->tstamp != INGRESS_FWDNS_MAGIC)