MFV r337020:9443 panic when scrub a v10 pool
illumos/illumos-gate@bb1f424574ac8e08069d0ba993c2a41ffe796794
Reviewed by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Andriy Gapon <avg@FreeBSD.org>
Reviewed by: Igor Kozhukhov <igor@dilos.org>
Approved by: Dan McDonald <danmcd@joyent.com>
Author: Matthew Ahrens <mahrens@delphix.com>