There was a misunderstanding whether to include them by default in
the dns.log, so remove them again.
There had also been a discussion and quirk that AD of a request would
always be overwritten by reply in the dns.log unless the reply is
missing. For now, let users extend dns.log themselves for what best
fits their requirements, rather than adding these flags by default.
Add a btest to print AD and CD flags for smoke testing still.
Parse authentic data (AD) and checking disabled (CD) bits according to
RFC 2535. Leaves the Z field as-is, in case users are already handling
this elsewhere and depend on the value being the integer for all 3 bits.
https://www.rfc-editor.org/rfc/rfc2535#section-6.1Fixes#2672
