4.9.28: VIA velocity hang: how to find cause?

[Udo van den Heuvel]

Hello,

I noticed multiple times that VIA velocity interface stop functioning
without reason but is revived after and `ifdown ethX; ifup ethX`.
No data is transferred until the `fix` is applied.
No errors are shown in dmesg or /var/log/messages w.r.t. the interface.
How to find the root cause?

This is with kernel 4.9.28.

Kind regards,
Udo