vsock/virtio: initialize vdev->priv before using VQs

vsock/virtio: initialize vdev->priv before using VQs

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit 4b5f1ad5566ada230aaa2ce861b28d1895f1ea68 ]

When we fill VQs with empty buffers and kick the host, it may send
an interrupt. `vdev->priv` must be initialized before this since it
is used in the virtqueue callbacks.

Fixes: 0deab087b16a ("vsock/virtio: use RCU to avoid use-after-free on the_virtio_vsock")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 10c6cb867ffa827a8364d0c481ec1438cd594652)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>