core: Fix the Network QoS unit translation

engine is using Megabits as units for the Network QoS 'Average' and
'Peak' properties.

vdsm is using Kilobytes for those properties.

current translation is wrong (1:1024). it should be 1:128

Change-Id: Ib299bc401aa9863717a663666d19ba1ae4ef3aba
Bug-Url: https://bugzilla.redhat.com/999799
Signed-off-by: Ofri Masad <omasad@redhat.com>