net/virtio-user: ignore result if status is unsupported

net/virtio-user: ignore result if status is unsupported

GET/SET STATUS is an optional feature, so it may not be negotiated. In
that case, the VIRTIO_GET_STATUS call will not update the status (given
as a pointer argument). Failing to identify this case would lead to
undefined behavior as the device status will be updated with the value
of a stack-allocated variable.

To fix this, return ENOTSUP if the feature is not supported and, in that
case, don't update device status.

Fixes: 44102e6298e7 ("net/virtio: check protocol feature in user backend")
Cc stable@dpdk.org

Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>