dnsdist: unify global stats accounting #6289
Clean up some statistics accounting which was handled inconsistently before:
Additional stats issues that this PR does not fix:
Similar to TCP handler, similar to cacheHits case.
Thanks! Code looks good, although I'm not sure we want to take the TCP response time into account in our latency calculations. It is my understanding that by design we only care about the UDP response time, especially because we use it for our policies, but I might be mistaken.