[Intel-wired-lan] igb: Random NIC down for 3-4 seconds and then UP

[manty kuma]

We see random NIC down like shown below. It lasts for a few seconds and
then the connection is back up.

>From kernel Log:
```
[ 3306.560431] igb 0000:03:00.0 enp3s0: igb: enp3s0 NIC Link is Down
[ 3309.532558] igb 0000:03:00.0 enp3s0: igb: enp3s0 NIC Link is Up 1000
Mbps Full Duplex, Flow Control: RX\/TX

[ 3337.380117] igb 0000:02:00.0 enp2s0: igb: enp2s0 NIC Link is Down
[ 3341.672189] igb 0000:02:00.0 enp2s0: igb: enp2s0 NIC Link is Up 100 Mbps
Half Duplex, Flow Control: None
```
Steps to reproduce: Unknown. Happens randomly
Frequency: once in a couple of weeks so far.

Kernel: 5.10
Firmware version: 3.25, 0x800005cf
driver: igb

Is it a known issue?
What can we do to better understand the reason for this behavior and fix it?
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