igmpproxy: Import patches from open-wrt / Telekom Labs

igmpproxy: Import patches from open-wrt / Telekom Labs

Major change in these patches for the user is the addition
of a whitelist item for up and downstream interfaces.

Excerpt from one of patches:

Defines a whitelist for multicast groups. The network address must be in the following
format 'a.b.c.d/n'. If you want to allow one single group use a network mask of /32,
i.e. 'a.b.c.d/32'.

By default all multicast groups are allowed on any downstream interface. If at least one
whitelist entry is defined, all igmp membership reports for not explicitly whitelisted
multicast groups will be ignored and therefore not be served by igmpproxy. This is especially
useful, if your provider does only allow a predefined set of multicast groups. These whitelists
are only obeyed by igmpproxy itself, they won't prevent any other igmp client running on the
same machine as igmpproxy from requesting 'unallowed' multicast groups.

You may specify as many whitelist entries as needed. Although you should keep it as simple as
possible, as this list is parsed for every membership report and therefore this increases igmp
response times. Often used or large groups should be defined first, as parsing ends as soon as
a group matches an entry.