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 <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/uapi/linux/if_ether.h

···
 #define ETH_P_ETHERCAT	0x88A4		/* EtherCAT			*/
 #define ETH_P_8021AD	0x88A8          /* 802.1ad Service VLAN		*/
 #define ETH_P_802_EX1	0x88B5		/* 802.1 Local Experimental 1.  */
-#define ETH_P_MXLGSW	0x88C3		/* MaxLinear GSW DSA [ NOT AN OFFICIALLY REGISTERED ID ] */
+#define ETH_P_MXLGSW	0x88C3		/* Infineon Technologies Corporate Research ST
+					 * Used by MaxLinear GSW DSA
+					 */
 #define ETH_P_PREAUTH	0x88C7		/* 802.11 Preauthentication */
 #define ETH_P_TIPC	0x88CA		/* TIPC 			*/
 #define ETH_P_LLDP	0x88CC		/* Link Layer Discovery Protocol */