DNSSEC will eventually become opt-out and when that happens
I'll add libnettle build-depends. For now, build with

fakeroot debian/rules DEB_BUILD_OPTIONS=usednssec

to get DNSSEC support.

The linux kernel treats all addresses with a limited lifetime as being
non permanent, but when taking over the prefix livetimes from
upstream assigned prefixes through DHCP, addresses will always have a limited
lifetime.

Still reject temporary addresses, as they indicate autoconfigured
interfaces.

Contributed by T-Labs, Deutsche Telekom Innovation Laboratories

Signed-off-by: Jonas Gorski<jogo@openwrt.org>