[virtio-queue] Support multiple working threads per queue #90
Description
Current Queue design only supports one working thread thread per queue, which may limit the throughput of the virtio backend device. For example, the virtio-fs only supports one queue per device for normal operations. On the otherwise, there are many synchronous blocking syscalls involved when serving virito-fs requests. So it would be beneficial to enhance the Queue design to support multiple working threads per queue.