[OPTIM] freq_ctr: do not rotate the counters when reading

[OPTIM] freq_ctr: do not rotate the counters when reading

It's easier to take the counter's age into account when consulting it
than to rotate it first. It also saves some CPU cycles and avoids the
multiply for outdated counters, finally saving CPU cycles here too
when multiple operations need to read the same counter.

The freq_ctr code has also shrinked by one third consecutively to these
optimizations.