in a layer 2 mesh network, multicast pings cause a lot of traffic in the
network, significantly increasing the 'backgroudn noise' (= Grundrauschen)
and stressing nodes in the network.

this commit blacklists all icmpv4 multicast traffic as well as multicast
icmpv6 echo-requests and node iformation queries. as no application
depending on these types of multicast traffic is known, blacklisting is safe.

Fixes https://github.com/freifunk-gluon/gluon/issues/311

gluon-ebtables-filter-multicast: allow hop-by-hop options as ICMPv6 is sometimes prefixed by an HBH header

the ports were interchanged, see the following packet flow:

client:546 --> [ff02::1:2]:547
server:547 --> client:546

therefore we need to allow outgoing multicast packets with dst-port 547
and unicast packets from bat0 to clients with dst-port 546 and 547 in the other direction