proto: Add some exotic ICMPv6 types

proto: Add some exotic ICMPv6 types

This adds support for matching on inverse ND messages as defined by
RFC3122 (not implemented in Linux) and MLDv2 as defined by RFC3810.

Note that ICMPV6_MLD2_REPORT macro is defined in linux/icmpv6.h but
including that header leads to conflicts with symbols defined in
netinet/icmp6.h.

In addition to the above, "mld-listener-done" is introduced as an alias
for "mld-listener-reduction".

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>