dntpd - Improve offset correction precision
* Offset corrections are more accurate with more samples (whereas frequency
corrections are more accurate when the first and last sample are far apart
in the time domain).
* Even though dntpd uses a standard deviation test to conditionalize offset
corrections, it is still possible to get false positives with only 4
samples.
* Once dntpd has gone into maintainance mode increase the number of
required samples for an offset correction from 4 to 8. This makes
the standard deviation more accurate, reduces false positives, and
improves stability.
* Retain the original mechanic during aquisition so dntpd applies corrections
sooner rather than later when first started.