MFC r348564: MFV r348552:
9682 page fault in dsl_async_clone_destroy() while opening pool

illumos/illumos-gate@ade2c82828f0dca1f46919aa1bd936ea1a5a0047

Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Sara Hartse <sara.hartse@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Serapheim Dimitropoulos <serapheim@delphix.com>