ULE vs. 4BSD in RELENG_7

[Josh Carroll]

> Turns out the last patch I posted had a small compile error because I
> edited it by hand to remove one section.  Here's an updated patch that
> fixes that and changes the min/max slice values to something more
> reasonable.  Slice min should be around 4 with a max of 12.
>
> Also looks like 4BSD's slice handling got more precise recently as well.
> jhb changed it from using a callout to an actual counter based on runtime.

ffmpeg runtime with the new patch: 1:39.09

buildworld: 13:55.689

Looks like things got a little worse with this patch. One thing of
note, the slice_min and slice values are:

kern.sched.slice_min: 5
kern.sched.slice: 13

Did I do something wrong to cause the slice min to be 5 instead of 4
and the max to be 13 instead of 12?

Thanks,
Josh