Description:
------------
FreeBSD supports listening on/joining both IPv4 and IPv6 multicast groups. However, it handles full RFC 3678 support (including IPv6) via a different interface (setsourcefilter vs setsockopt).

In order to properly support multicast on FreeBSD (including IPv6 support), one would have to (conditionally) use setsourcefilter instead of setsockopt (throughout much of ext/sockets/multicast.c).

Since I don't have the requirement or will to implement this with FreeBSD's newer protocol agnostic sourcefilter APIs, I've chosen to take the easy way out and just make it work with IPv4 only.

This bug report should likely be split into two bugs as I've only addressed the IPv4 case for now.

I've included versions that correspond to my environment. However, this is far more generally applicable.

This bug is the FreeBSD variant/equivalent of bug #63000 (which was for macOS).

Please see the following FreeBSD documentation references (for details on FreeBSD's multicast support):

https://www.freebsd.org/cgi/man.cgi?query=ip&apropos=0&sektion=4&manpath=FreeBSD+12-current&arch=default&format=html
https://www.freebsd.org/cgi/man.cgi?query=sourcefilter&sektion=3&apropos=0&manpath=FreeBSD+12-current

Test script:
---------------
<?php

// This just listens for MDNS traffic. You could optionally dispatch a query if your test network doesn't have a bunch of MDNS traffic

$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
if (!socket_set_option($socket, IPPROTO_IP, MCAST_JOIN_GROUP, array('group' => '224.0.0.251', 'interface' => 0))) {
	echo socket_strerror(socket_last_error());
}
socket_set_option($socket, SOL_SOCKET, SO_REUSEPORT, 1);
socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1);
socket_set_option($socket, SOL_SOCKET, SO_RCVTIMEO, ['sec' => 10, 'usec' => 0]);
socket_bind($socket, '0.0.0.0', 5353);

// socket_sendto($socket, $data, strlen($data), 0, '224.0.0.251', 5353);

$response = socket_read($socket, 1024, PHP_BINARY_READ);
var_dump($response);

Expected result:
----------------
true (and actually seeing multicast packets destined for the requested group address)

Actual result:
--------------
false (with a pass-through error message referencing code [22]/EINVAL)