Please support qemu/kvm virtio devices

```
The qemu and KVM virtual machines can provide 9p filesystems (and other 
devices) via their internal "virtio" interface, which provides a PCI Express 
device with a low-overhead communication channel to the VM.  Please consider 
adding support for virtio 9P filesystems in ninefs.
```

Original issue reported on code.google.com by `josh@joshtriplett.org` on 26 Jun 2012 at 8:35
