ebtables-filter-mcast: Remove redundant allow-filter for hop-by-hop

ebtables actually skips any IPv6 extension headers like the hop-by-hop
one. So this rule is actually void.

The intend back then was to allow passing MLD messages into the mesh.
Since extension headers are skipped, the general icmpv6 rule will
actually match MLD messages. So the hop-by-hop rule is unnecessary,
too.

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