In an earlier world order, UMA would flush per-CPU statistics to the

In an earlier world order, UMA would flush per-CPU statistics to the
zone whenever it was moving buckets between the zone and the cache,
or when coalescing statistics across the CPU.  Remove flushing of
statistics to the zone when coalescing statistics as part of sysctl,
as we won't be running on the right CPU to write to the cache
statistics.

Add a missed gathering of statistics: when uma_zalloc_internal()
does a special case allocation of a single item, make sure to update
the zone statistics to represent this.  Previously this case wasn't
accounted for in user-visible statistics.

MFC after:	1 week