How to create an ICMP source quench message packet using RAW socket in C?

Question

I want to send an ICMP Source Quench packet(type-4, code-0) using SOCK_RAW in C. According to this link, they said

This packet contains no extra header except the data portion, which contains the internet header plus 64 bits of the original data datagram. This is used to match the source quench message to the correct process, which is currently sending data through the gateway or to the destination host.

This is an implementation of icmp echo message.

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <arpa/inet.h>

#include "myheader.h"

unsigned short in_cksum (unsigned short *buf, int length);
void send_raw_ip_packet(struct ipheader* ip)
{
   struct sockaddr_in dest_info;
   int enable = 1;

   // Step 1: Create a raw network socket.
   int sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

   // Step 2: Set socket option.
   setsockopt(sock, IPPROTO_IP, IP_HDRINCL,
                 &enable, sizeof(enable));

   // Step 3: Provide needed information about destination.
   dest_info.sin_family = AF_INET;
   dest_info.sin_addr = ip->iph_destip;

   // Step 4: Send the packet out.
   sendto(sock, ip, ntohs(ip->iph_len), 0,
       (struct sockaddr *)&dest_info, sizeof(dest_info));
   close(sock);
}

/******************************************************************
Spoof an ICMP echo request using an arbitrary source IP Address
*******************************************************************/
int main() {
  char buffer[1500];

  memset(buffer, 0, 1500);

  /*********************************************************
  Step 1: Fill in the ICMP header.
  ********************************************************/
  struct icmpheader *icmp = (struct icmpheader *)
                         (buffer + sizeof(struct ipheader));
  icmp->icmp_type = 8; //ICMP Type: 8 is request, 0 is reply.

  // Calculate the checksum for integrity
  icmp->icmp_chksum = 0;
  icmp->icmp_chksum = in_cksum((unsigned short *)icmp,
                             sizeof(struct icmpheader));

  /*********************************************************
  Step 2: Fill in the IP header.
  ********************************************************/
  struct ipheader *ip = (struct ipheader *) buffer;
  ip->iph_ver = 4;
  ip->iph_ihl = 5;
  ip->iph_ttl = 20;
  ip->iph_sourceip.s_addr = inet_addr("1.2.3.4");
  ip->iph_destip.s_addr = inet_addr("10.0.2.69");
  ip->iph_protocol = IPPROTO_ICMP;
  ip->iph_len = htons(sizeof(struct ipheader) +
                   sizeof(struct icmpheader));

  /*********************************************************
  Step 3: Finally, send the spoofed packet
  ********************************************************/
  send_raw_ip_packet (ip);

  return 0;
}

How to add the data portion in ICMP packet to create source quench message?