RE: Ethtool is missing C2C link modes

After evaluating the current trends in C2C use-cases (for 10G & higher,
especially the latest gen firmware orchestrated high speed PAM4
signaling), and distinguishing between the ethtool link mode and
the phy_interface_t, we think the ethtool link-mode is still the
correct fit for C2C protocol to model it as the electrical domain
channel/media for establishing links over the following primary use-cases.

 1. System-A <== C2C ==> System-B
    Direct connection with no intermediates. This is clean replacement of
    KR link and user can choose to operate the ethernet interface at all
    various speed and modes of link that exists in KR.

 2. C2C as simplified KR with fixed speed & low reach => no need of ANLT
    The on-board copper-electrical trace interfaces are so well designed,
    and optimized to operate for particular speed by offloading the
    analog signal integrity into the on-board "redriver" chip like
    TI's DS560MB410 or DS560DF410 - like the electrical repeater

- Thank you,
Siddaraju D H