IPv6 hton layout does not match ipv6_mreq

Given this C program:

#include <netinet/in.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char * argv[])
{
        struct ipv6_mreq req;
        memset(&req, 0, sizeof(req));
	req.ipv6mr_multiaddr.s6_addr[0] = 0xFF;
	req.ipv6mr_multiaddr.s6_addr[1] = 0x02;
	req.ipv6mr_multiaddr.s6_addr[15] = 0xFB;

        uint8_t * ptr = (uint8_t *)&req;
        for(int i = 0; i < sizeof(req); i++) {
                fprintf(stderr, "\\%#02x", ptr[i]);
        }

        fprintf(stderr, "\n");
        return 0;
}

The bytes of the ipv6_mreq struct are: \0xff\0x2\00\00\00\00\00\00\00\00\00\00\00\00\00\0xfb\00\00\00\00

However, if I use this Ruby program:

require "ipaddr"

p IPAddr.new("ff02::fb").hton

The bytes are: "\xFF\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xFB"

I think hton should match the ipv6_mreq layout.

The issue names IPAddr#hton and the C ipv6_mreq structure; start by locating the hton implementation and existing tests in the ipaddr repository, then compare the two representations' byte lengths and layouts. Done means the expected relationship between hton and ipv6_mreq is decided and documented by a regression test or a clearly justified behavior change.