generic_config_updater.test_eth_interface::test_eth_interface_admin_change left Ethernet0 oper down on testbed about sonic-mgmt

[bingwang-ms]

Same issue was found on other testbeds. The issue was because the FEC mode of Ethernet0 is not recovered after the test running.

[isabelmsft]

This issue is not related to GCU.

The issue can be reproduced directly using sonic-db-cli as follows:

Before fec configuration change:
admin@SONIC:~$ show int status
Interface Lanes Speed MTU FEC Alias Vlan Oper Admin Type Asym PFC

---

 Ethernet0              0,1      50G   9100     N/A    etp1a           trunk          up            up  QSFP28 or later         off

Change fec configuration via sonic-db-cli:
admin@SONIC:~$ sonic-db-cli CONFIG_DB HSET "PORT|Ethernet0" "fec" "rs"

After fec configuration change:
admin@SONIC:~$ show int status
Interface Lanes Speed MTU FEC Alias Vlan Oper Admin Type Asym PFC

---

 Ethernet0              0,1      50G   9100     rs    etp1a           trunk    down       up  QSFP28 or later         off

Oper status remains down.

@prgeor , could you please help investigate the behavior above? Is this behavior expected, and why does it only happen on some SKU (e.g. Mellanox-SN3800) but not others (e.g. msn2700)?