This patch introduces a vhost-user device for vsock, using the
vhost-vsock-common parent class.

The vhost-user-vsock device can be used to implement the virtio-vsock
device emulation in user-space.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20200522122512.87413-3-sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>