Ethtool is missing C2C link modes

Hello Linux Ethernet team, Maxime, Andrew & Michal,

The IEEE AUI chip-to-chip (C2C) is the accepted standard for connecting
chips that handle subfunctions within the OSI physical layer. Just to
pick, the C2C is widely used when connecting Ethernet SoCs with retimers
and PCS SerDes terminated external-phys to offload PHY sublayer functions.

With the existing ethtool link modes, we were not able to fit these C2C
interfaces on any others (we fitted **SGMII interfaces to baseT link modes)
and we see this as a gap. If you acknowledge this, we plan to send an
RFC patch to define below listed C2C link modes to ethtool.

	10G_SFI_C2C		SFF-8418
	25G_AUI_C2C		IEEE 802.3 Annex 109A
	CAUI4 C2C		IEEE 802.3 Annex 83D
	LAUI2-C2C		IEEE 802.3 Annex 135B
	50GAUI-1 C2C		IEEE 802.3 Annex 135F
	200GAUI-4 C2C		IEEE 802.3 Annex 120D
	100GAUI-1 C2C		IEEE 802.3ck Annex 120F
	200GAUI-2 C2C		IEEE 802.3ck Clause 162
	400GAUI-4 C2C		IEEE 802.3ck Clause 163

- Thank you,
Siddaraju D H