Don't reply to DHCPv6 SOLICIT messages if we're not
configured to do stateful DHCPv6. Thanks to Win King Wan
for the patch.

Fix broken DNSSEC validation of ECDSA signatures.

Add --dnssec-timestamp option, which provides an automatic
way to detect when the system time becomes valid after boot
on systems without an RTC, whilst allowing DNS queries before the
clock is valid so that NTP can run. Thanks to
Kevin Darbyshire-Bryant for developing this idea.