virtio-net: handle virtio_net_flush_tx() errors

virtio-net: handle virtio_net_flush_tx() errors

All these errors are caused by a buggy guest: let's switch the device to
the broken state instead of terminating QEMU. Also we detach the element
from the virtqueue and free it.

If this happens, virtio_net_flush_tx() also returns -EINVAL, so that all
callers can stop processing the virtqueue immediatly.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>