Illumos #3120 zinject hangs in zfsdev_ioctl() due to uninitialized zc

3120 zinject hangs in zfsdev_ioctl() due to uninitialized zc

Reviewed by: Richard Lowe <richlowe@richlowe.net>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/issues/3120
  illumos/illumos-gate@f4c46b1eda9212fd32ba197043d52239ef5c0a7f

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2152