Previous code tried to keep prefetch streams while moving dnode. But
it was at least not updating per-stream zs_fetchback pointers, causing
use-after-free on next access. Instead of that I see much easier and
cleaner to just drop old prefetch state and start new from scratch.
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes#11936Closes#11998
0db64e9036