vdpa: move vhost reset after get vring base

vdpa: move vhost reset after get vring base

The function vhost.c:vhost_dev_stop calls vhost operation
vhost_dev_start(false). In the case of vdpa it totally reset and wipes
the device, making the fetching of the vring base (virtqueue state) totally
useless.

The kernel backend does not use vhost_dev_start vhost op callback, but
vhost-user do. A patch to make vhost_user_dev_start more similar to vdpa
is desirable, but it can be added on top.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230303172445.1089785-8-eperezma@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>