r8169: fix rare issue with broken rx after link-down on RTL8125

r8169: fix rare issue with broken rx after link-down on RTL8125

In very rare cases (I've seen two reports so far about different
RTL8125 chip versions) it seems the MAC locks up when link goes down
and requires a software reset to get revived.
Realtek doesn't publish hw errata information, therefore the root cause
is unknown. Realtek vendor drivers do a full hw re-initialization on
each link-up event, the slimmed-down variant here was reported to fix
the issue for the reporting user.
It's not fully clear which parts of the NIC are reset as part of the
software reset, therefore I can't rule out side effects.

Fixes: f1bce4ad2f1c ("r8169: add support for RTL8125")
Reported-by: Martin Kjær Jørgensen <[email protected]>
Link: https://lore.kernel.org/netdev/[email protected]/T/
Signed-off-by: Heiner Kallweit <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>