engine: Fix NPE when network qos is partially provided

The patch fixes NPE caused by autoboxing of a none-set
network-qos attribute (i.e. inbound average).

Change-Id: I483dbab4d5a2b89b5ee2290fdfe09f65ddfac0bd
Bug-Url: https://bugzilla.redhat.com/1000810
Signed-off-by: Moti Asayag <masayag@redhat.com>