Use STAILQ instead of TAILQ for bucket lists. We only need FIFO behavior
and this is more space efficient.

Stop queueing recently used buckets to the head of the list. If the bucket
goes to a different processor the cache coherency will be more expensive.
We already try to encourage cache-hot behavior in the per-cpu layer.

Reviewed by: rlibby
Differential Revision: https://reviews.freebsd.org/D23493