Illumos 4975 - missing mutex_destroy() calls in zfs

4975 missing mutex_destroy() calls in zfs
Author: Jorgen Lundman <lundman@lundman.net>
Reviewed by: Matthew Ahrens <matthew.ahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Rich Lowe <richlowe@richlowe.net>
Reviewed by: Seth Nimbosa <darth.Serious@gmail.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Don Brady <dev.fs.zfs@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>

References:

https://www.illumos.org/issues/4975
https://github.com/illumos/illumos-gate/commit/d2b3cbb

Ported-by: Chris Dunlop <chris@onthe.net.au>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>