Clarifying section "2.6.12 virtqueue Operation" in virtio-v1.1

Fixes:Âhttps://github.com/oasis-tcs/virtio-spec/issues/43

We'd like to propose clarifying the usage ofÂpacketsÂandÂbuffersÂin section "2.6.12 virtqueue operation" as described in the github issue above.

Thanks.Â