This patch moves async-related metadata from vhost_virtqueue
to a dedicated struct. It makes it clear which fields are
async related, and also saves some memory when async feature
is not in use.
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Reviewed-by: Jiayu Hu <jiayu.hu@intel.com>