net: add multiqueue support

Multiqueue feature was supported by kernel/qemu upstream already,
this patch changed Autotest to support command line.

This change compat 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

Signed-off-by: Amos Kong <akong@redhat.com>
net: update hotplug tests

Signed-off-by: Amos Kong <akong@redhat.com>