net: add multiqueue support (just send it out, will do more test in the weekend)

Multiqueue feature was supported by kernel/qemu upstream already,
this patchset changed Autotest to support command line.

This change compat with old qemu/kernel, it will still use 'fd' when
there is only one queue.

More information about multiqueue:
  http://www.linux-kvm.org/page/Multiqueue
  linux/Documentation/networking/tuntap.txt