vsock/virtio: read the negotiated features before using VQs

Complete the driver configuration, reading the negotiated features,
before using the VQs in the virtio_vsock_probe().

Fixes: 53efbba1

 ("virtio/vsock: enable SEQPACKET for transport")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>