[marif-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

On a VOQ switch, the agent requires a nodeMac on its own dsfNodes entry and stops at config load without one. A platform's default agent.conf is shared by every unit, so it cannot carry that per-unit MAC. When fboss_init.sh creates agent.conf, it now runs the new set_dsf_node_mac.py, which writes the chassis EEPROM's Switch ASIC MAC Base into each local dsfNodes entry without a nodeMac, and into the matching switchMac when that is unset too. The script reads the CHASSIS_EEPROM_PARSED file that platform_manager writes. Configs without a local DSF node are left unchanged, and an existing agent.conf is never rewritten.

Test Plan

On a m4340nhp device without an agent.conf, fboss_init creates one with the unit's MAC as nodeMac and switchMac, and the agents start and bring up all 64 front-panel ports. A second run leaves the file unchanged, and the script leaves an NPU config untouched.