Make !NETFILTER_ADVANCED enable IP6_NF_MATCH_IPV6HEADER

We want IPV6HEADER matching for the non-advanced default netfilter
configuration, since it's part of the standard netfilter setup of at
least some distributions (eg Fedora).

Otherwise NETFILTER_ADVANCED loses much of its point, since even
non-advanced users would have to enable all the advanced options just to
get a working IPv6 netfilter setup.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>