dnsdist: Speed up response content matching

dnsdist: Speed up response content matching

This commit introduces a new method to compare a `DNSName`
against a view of raw, wire-format bytes, skipping the
allocation and copy that is usually required to get a
second `DNSName` object to compare against.
This signifitcantly reduces the amount of time matching
a DNS response received from a backend against the content
we expect to find.

Signed-off-by: Remi Gacogne <remi.gacogne@powerdns.com>