Illumos 4901 - zfs filesystem/snapshot limit leaks

4901 zfs filesystem/snapshot limit leaks
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>

References:

https://www.illumos.org/issues/4901
https://github.com/illumos/illumos-gate/commit/adf3407

Ported by: Brian Behlendorf <behlendorf1@llnl.gov>