net: remove redundant evaluation

Valid ifname is provided and used in open_tap(), the
evaluation in the end is redundant, just remove it.

Signed-off-by: Amos Kong <akong@redhat.com>
add definitions of multiqueue

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

This patch just makes the cases work. I will change cases really
use multi_queue by another split patchset.

Signed-off-by: Amos Kong <akong@redhat.com>
virttest.asset: Pass on restore_image value

With the work made on the asset library, we forgot to
pass the force param to asset.download_file(), as a
result the test runner --restore-image flag stopped
working.

So fix the problem by passing the appropriate option
to that function.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>