K 10
svn:author
V 3
avg
K 8
svn:date
V 27
2017-10-19T16:36:07.342966Z
K 7
svn:log
V 673
remove spa_sync_on assert from spa_async_thread_vd

Unlike spa_async_thread that can get started only from spa_sync()
spa_async_thread_vd can get started from other contexts.
Additionally, spa_async_thread_vd does not really depend on
spa sync being enabled.

The incorrect assert could be triggered by importing a pool in the
read-only mode and then disconnecting one of its disks.
In this case spa_sync_on was false because the pool was read-only
and spa_async_thread_vd was started to handle SPA_ASYNC_REMOVE event.

Note: spa_async_thread_vd() currently exists only in FreeBSD, it was
split out of spa_async_thread() in r253990.

Discussed with:	mav
MFC after:	2 weeks

END