Add two new dedicated fields to provide the ICMPv6 code and type. While
libnetfilter_conntrack uses the same attribute for both ICMPv4 and v6,
there are no version-agnostic ICMP IEs in IPFIX.
The fields are annotated with the appropriate IPFIX metadata, which is
currently not actually used anywhere. You may call it consistency,
future-proofing or cargo-culting.
Signed-off-by: Corubba Smith <corubba@gmx.de> Signed-off-by: Florian Westphal <fw@strlen.de>