Simplify Cache DB RRset type statistic counters
See comments here: !2237 (comment 72162)
Ondřej Surý: How much memory would it mean to use 8 bits for rrtypes, and the rest would be a bit field?
That would be: 1 bit for others 1 bit for nxrrset 1 bit for nxdomain 1 bit for stale 1 bit for ancient
That's 8129 values for 13 bits, and 16384 for 14 bits, both are lower then 2^16-1 which we are still using as ncounters.
The arithmetics is currently a brain twister.