if_ether.h: Clarify ethertype validity for gsw1xx dsa

if_ether.h: Clarify ethertype validity for gsw1xx dsa

This 0x88C3 is registered to Infineon Technologies Corporate Research ST
and are used by MaxLinear.
Infineon made a spin off called Lantiq.
Lantiq was acquired by Intel
MaxLinear acquired Intels Connected Home division.

The product FAQ from MaxLinear describes it's history from the F24S.
The driver for the gsw1xx is based on Lantiq showing it's similarities.

Ref https://standards-oui.ieee.org/ethertype/eth.txt

Signed-off-by: Peter Enderborg <Peter.Enderborg@axis.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>