gluon-ebtables-filter-multicast: drop icmpv6 type 128 & 139, drop icmp

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.

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/110-mcast-allow-icmp

-rule 'MULTICAST_OUT -p IPv4 --ip-protocol icmp -j RETURN'

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/110-mcast-allow-icmpv6

-rule 'MULTICAST_OUT -p IPv6 --ip6-protocol 0 -j RETURN' -- hop-by-hop
+rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type echo-request -j DROP'
+rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp --ip6-icmp-type 139 -j DROP'
 rule 'MULTICAST_OUT -p IPv6 --ip6-protocol ipv6-icmp -j RETURN'
+
+rule 'MULTICAST_OUT -p IPv6 --ip6-protocol 0 -j RETURN' -- hop-by-hop