UDP_PAYLOAD_BYTES
iph->tot_len = htons(sizeof(*iph) + sizeof(*udph) + UDP_PAYLOAD_BYTES);
udph->len = htons(sizeof(*udph) + UDP_PAYLOAD_BYTES);
memset(udph + 1, 0xAA, UDP_PAYLOAD_BYTES);
tx_desc->len = sizeof(*eth) + sizeof(*iph) + sizeof(*udph) + UDP_PAYLOAD_BYTES;
char udp_payload[UDP_PAYLOAD_BYTES];
memset(udp_payload, 0xAA, UDP_PAYLOAD_BYTES);
err = sendto(sock_fd, udp_payload, UDP_PAYLOAD_BYTES, MSG_DONTWAIT,