qemu: Set default qdisc before setting bandwidth

qemu: Set default qdisc before setting bandwidth

While the code that's setting default qdisc is clever enough to
not overwrite any bandwidth (potentially) set by
virNetDevBandwidthSet() (and thus the root qdisc htb is not
replaced with noqueue), it does print a debug message when that's
the case. It's needless. We can set the root qdisc beforehand and
let virNetDevBandwidthSet() overwrite it.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>