Illumos #3836

3836 zio_free() can be processed immediately in the common case
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Approved by: Dan McDonald <danmcd@nexenta.com>

References:

https://www.illumos.org/issues/3836
illumos/illumos-gate@9cb154a3c9f170904dce9bad5bd5a7d256b922a4

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1775