qcacld-3.0: Fix the UDP qos upgrade logic

The UDP qos upgrade is skipped currently if the setting
from userspace is set to best effort. Also with the current
logic the priority of packets at "best effort" gets
downgraded to "background".

Fix the UDP qos upgrade logic to take care of using
the "background" priority value as a trigger to skip
UDP qos upgrade.

Change-Id: I5111a930995ddd71b082db95440ed778f09a3cba
CRs-Fixed: 2816426