While testing and automating [1] for QoS router gateway feature (OSPRH-2909), it seems FIPs and router gateways were not destined to work with QoS DSCP rules at all at this point but happened to work correctly, as seen in [1] existing code to test DSCP with FIP, and new added code to test DSCP enforcement with router gateways (with precedence checked for both network/port QoS DSCP).

After consulting with rodolfo_alonso about the automation patch, I understood from the chat that the proper precedence should be at least verified and documented properly for customers (documentation bug).

[1] 954372: Test QoS DSCP for router gateways | https://review.opendev.org/c/x/whitebox-neutron-tempest-plugin/+/954372