core: Update host network QoS supported version to 3.6

It used to be 3.4, but due to shortcomings of libvirt it is only made
available in 3.6.

Change-Id: I8bb61c373cb99f36e00d913dd61afc3b33ae34eb
Signed-off-by: Lior Vernia <lvernia@redhat.com>