vhost: move acked_features to VQs

Refactor code to make sure features are only accessed
under VQ mutex. This makes everything simpler, no need
for RCU here anymore.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --cc drivers/vhost/net.c
Simple merge

diff --cc drivers/vhost/scsi.c
Simple merge

diff --cc drivers/vhost/test.c
Simple merge

diff --cc drivers/vhost/vhost.c
Simple merge

diff --cc drivers/vhost/vhost.h
Simple merge