prepare_ip4ip has a bug？

[liuqi-sun]

void prepare_ip4ip (packetinfo *pi)
{
packetinfo pipi;
memset(&pipi, 0, sizeof(packetinfo));
config.pr_s.ip4ip_recv++;
pipi.pheader = pi->pheader;
pipi.packet = (pi->packet + pi->eth_hlen + (IP_HL(pi->ip4) * 4));
pipi.end_ptr = pi->end_ptr;
if (pi->ip4->ip_p == IP_PROTO_IP4) {
prepare_ip4(&pipi);
parse_ip4(&pipi);
return;
} else {
prepare_ip6(&pipi);
parse_ip6(&pipi);
return;
}
}

In prepare_ip4(&pipi) function，pi->ip4 = (ip4_header *) (pi->packet + pi->eth_hlen) ，why add pi->eth_hlen？pi->packet is IP4 message.