vhost/test: stop device before reset

[ Upstream commit 245cdd9fbd396483d501db83047116e2530f245f ]

When device stop was moved out of reset, test device wasn't updated to
stop before reset, this resulted in a use after free.  Fix by invoking
stop appropriately.

Fixes: b211616d ("vhost: move -net specific code out")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>