Request for SAI capability check to determine the Ingress/Egress DSCP/TC action precedence supported by the ASIC.

[siqbal1986]

Based on the community feedback during the review of the document SAI Egress DSCP action behavior (#2049). a suggestion was presented to creata a new SAI capibility API to check the precendence of DSCP/TC actions by the ASIC.
e.g.
In the above mentioned document, the default precedence of the Egress DSCP action set by various components is given as the following.

1. Egress ACL.
2. Tunnel DSCP mapping
   • Tunnel TC-COLOR -> DSCP mapping
   • Tunnel DSCP mode
   • Switch Tunnel TC-COLOR -> DSCP map
3. Port Qos TC-COLOR -> DSCP map
4. Switch Qos TC-COLOR -> DSCP map

However based on the HW pipeline layout, a perticular ASIC may follow a different order of precedence.
In such a case a SAI query would be helpful in determining the order of precedence used by the ASIC.