Revert "Return -1 from arc_shrinker_func()"

This reverts commit c11a12bc3b2e5ee9a6bd74e26f1a396b6025fbd4.

Out of memory events were fixed by reverting this patch.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
When at the limit, evict "data" before "metadata"

Work in progress. I will add a more detailed commit message soon.

Signed-off-by: Prakash Surya <surya1@llnl.gov>