gluon-ebtables-filter-multicast: allow respondd queries (#2103)

This allows running a respondd querier and map server behind a Gluon
node.

For instance at Freifunk Lübeck we now moved the map server
behind a Gluon VM and removed batman-adv and fastd from the
map server VM to reduce the maintenance work.

Increased multicast overhead should be minimal / non existent, as it is
unlikely to accidentally have respondd queriers running behind a Gluon
node.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>