Further UMA statistics related changes:

• Add a new uma_zfree_internal() flag, ZFREE_STATFREE, which causes it to to update the zone's uz_frees statistic. Previously, the statistic was updated unconditionally.

• Use the flag in situations where a "real" free occurs: i.e., one where the caller is freeing an allocated item, to be differentiated from situations where uma_zfree_internal() is used to tear down the item during slab teardown in order to invoke its fini() method. Also use the flag when UMA is freeing its internal objects.

• When exchanging a bucket with the zone from the per-CPU cache when freeing an item, flush cache statistics back to the zone (since the zone lock and critical section are both held) to match the allocation case.

MFC after: 3 days