raw_checksum
sum = raw_checksum((uint8_t *)&iphdr->ip_src, 2 * sizeof(iphdr->ip_src),
sum = raw_checksum((uint8_t *)udphdr, UDP_HLEN, sum);
sum = raw_checksum((uint8_t *)udp_payload, payload_len, sum);
sum = raw_checksum((uint8_t *)&iphdr->ip6_src, 2 * sizeof(iphdr->ip6_src),
sum = raw_checksum((uint8_t *)&udphdr->len, sizeof(udphdr->len), sum);
sum = raw_checksum((uint8_t *)udphdr, UDP_HLEN, sum);
sum = raw_checksum((uint8_t *)udp_payload, payload_len, sum);