r8169: re-establish support for RTL8401 chip version

r8169 never had native support for the RTL8401, however it reportedly
worked with the fallback to RTL8101e [0]. Therefore let's add this
as an explicit assignment.

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=956868

Fixes: b4cc2dcc

 ("r8169: remove default chip versions")
Reported-by: Camaleón <noelamac@gmail.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>