evaluate: enforce ip6 proto with exthdr expression

evaluate: enforce ip6 proto with exthdr expression

Don't allow use of exthdr with e.g. ip family.
Move frag.t to ip6 directory and don't use it with ipv4 anymore.

This change causes major test failures for all exthdr users
since they now fail with inet/bridge/netdev families.

Will be resolved in a later patch -- we need to add
an ipv6 dependency for them.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>