[RFC/PATCH] Add a socketoption IPV6_MULTICAST_ALL analogue to the IPV4 version

[Andre Naujoks]

Hi.

I was running into a problem, when trying to join multiple multicast groups
on a single socket and thus binding to the any-address on said socket. I
received traffic from multicast groups, I did not join on that socket and
was at first surprised by that. After reading some old e-mails/threads,
which came to the conclusion "It is, as it is."
(e.g https://marc.info/?l=linux-kernel&m=115815686626791&w=2), I discovered
the IPv4 socketoption IP_MULTICAST_ALL, which, when disabled, does exactly
what I would expect from a socket by default.

I propose a socket option for IPv6, which does the same and has the same
default as the IPv4 version. My first thought was, to just apply
IP_MULTICAST_ALL to a ipv6 socket, but that would change the behavior of
current applications and would probably be a big no-no.

Regards
  Andre