Illumos #3973

3973 zfs_ioc_rename alters passed in zc->zc_name
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>

References:

https://www.illumos.org/issues/3973
illumos/illumos-gate@a0c1127b147dc6a0372b141deb8c0c2b0195b8ea

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