dnsdist: Fix the wrong RD and CD flags being cached, causing misses

dnsdist: Fix the wrong RD and CD flags being cached, causing misses

We used to restore the RD and CD flags from the initial query before
inserting the response into the cache. That would cause an issue
if the flags had been altered, for example via SetNoRecurseAction,
as the cache lookup is done _after_ the actions have been applied
and thus after the flags altered.
If the initial query had the RD bit set, and thus was cleared by the
rule, the response would have been inserted with the RD bit restored,
and no lookup would then succeed because it would be done with the
bit cleared.
This commit fixes the insertion to use the RD and CD bits as set in
the response before restoring them, and restores the RD and CD bits
after a cache hit as well, to ensure that:
- cache lookups are done after the rules are applied
- cache insertions are done before the flags are restored