virtio_ring: add a func argument 'recycle_done' to virtqueue_reset()

When virtqueue_reset() has actually recycled all unused buffers,
additional work may be required in some cases. Relying solely on its
return status is fragile, so introduce a new function argument
'recycle_done', which is invoked when it really occurs.

Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>