If the user selects bothTagDscp(4), and a packet arrives
with both DSCP and a Vlan tag, the DSCP priority system will
take precedence.
tagOnly(3) will use Layer 2 Vlan Priority bits to assign a
Service
Level Class (SLC) to a packet and tagMappingTable
information will be used.
dscpOnly(2) will use Layer 3 DSCP bits to assign an SL class
to a packet.
dscpMappingTable information will be used