Fix for additional interface flap during fast-reboot on platforms due to delayed serdes programming

[tjchadaga]

Why I did it

During fast-reboot, delayed serdes programming done after transceiver detection results in additional interface flap and traffic loss exceeding the required 30s (Issue: #9165)

How I did it

Fix includes:

1. making a backup of media settings from appdb during fast-reboot (Dump media_settings from appDB during fast-reboot sonic-utilities#1910)
2. loading this to redis after the switch boots up (this PR).
3. Configuration of serdes triggered by reading media_settings.json file is skipped (Skip loading media config from media_settings.json for fast-reboot sonic-platform-daemons#221)

How to verify it

Run advanced_reboot/test_advanced_reboot.py::test_fast_reboot on 9332 or similar platform that use media_settings.json and ensure that

• no additional interface flap is seen during fast-reboot
• TRANSCEIVER_INFO & SERDES objects are populated in state and asic db as expected

2021-11-03 17:20:14 : Summary:
2021-11-03 17:20:14 : --------------------------------------------------
2021-11-03 17:20:14 : Longest downtime period was 0:00:15.611417
2021-11-03 17:20:14 : Reboot time was 0:00:57.564040
2021-11-03 17:20:14 : Expected downtime is less then 0:00:30
2021-11-03 17:20:14 : --------------------------------------------------
2021-11-03 17:20:14 : Additional info:
2021-11-03 17:20:14 : --------------------------------------------------
2021-11-03 17:20:14 : INFO:172.16.142.69:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.68:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.70:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.71:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.65:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.64:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.67:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : INFO:172.16.142.66:PortChannel interface state changed 1 times
2021-11-03 17:20:14 : --------------------------------------------------
2021-11-03 17:20:14 : ==================================================

UT logs:

UT_logs_advanced_reboot.log
fast-reboot.log

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)