wlan: Map DSCP 46 (EF) to Voice Userpriority

Currently the default QOS mapping maps DSCP 46 to BE traffic.
However DSCP 46 is defined by RFC 2598 to be an Expedited
Forwarding per-hop behavior, and this DSCP value is utilized
for VoIP services. Due to this mapping voice traffic is sent
as best effort. Hence marking it to Voice traffic.

Change-Id: I5538934624888d53e927f2da8aa2d1f4c8b9db4c
CRs-fixed: 2931144