This is the from-value in the tablemap. If
cbQosTableMapCfgBehavior equals to either copy(2) or
ignore(3), when the content in the from-type(e.g.,
cbQosTMSetIpDscpFromType) equals to this value, the
value in the to-type(e.g., IpDscp) will be set to
cbQosTableMapValueCfgTo. Each tablemap can configure
multiple from-value/to-value pairs.