ethtool: link 10000baseCR to SFF-8431, Appendix-E SFP+ DA

Add comment to clarify the physical media 10000baseCR follows.

10000baseCR does not correspond to any IEEE 802.3 *base-CR PMD.
It has no autonegotiation, no link training, and no mandatory FEC.
The industry standard for this media type is SFF-8431 Appendix-E
Direct Attach cable, also known as 10G_SFI_DA.

Link: https://lore.kernel.org/r/SN7PR11MB69003D33489DB1D6B17EF72A9AF52@SN7PR11MB6900.namprd11.prod.outlook.com

Signed-off-by: Siddaraju DH <siddaraju.dh@intel.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260703100537.1109838-1-siddaraju.dh@intel.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>