Convert DNS_GETDB_ into struct with 1-bit long booleans

See !8683 (comment 433377) for details:

Going step further, I think it can very well be a struct with booleans. It should cost nothing because compiler is not stupid nowadays and it will make decoding values in coredumps easier.

(To be clear - I mean something like this: !6902 (merged) (merged))

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