dnsdist: Cache based on the DNS flags of the query after applying the rules

dnsdist: Cache based on the DNS flags of the query after applying the rules

The tentative fix in dbadb4d272a3317407e6bc934f55c2d41a87c0ac actually
introduced an issue, because the backend might not perfectly echo the
RD and CD flags as they were in the query.
We can't use the "original" (before applying rules) flags either, so
we need to store the flags as they were sent to the backend to be
able to correctly store them in the cache.