net: ethtool: Add impedance mismatch result code to cable test

net: ethtool: Add impedance mismatch result code to cable test

Some PHYs can recognize during a cable test if the impedance in the cable
is okay. They can detect reflections caused by impedance discontinuity
between a regular 100 Ohm cable and an abnormal part with a higher or
lower impedance.

This commit introduces a new result code:
ETHTOOL_A_CABLE_RESULT_CODE_IMPEDANCE_MISMATCH,
which represents the results of a cable test indicating issues with
impedance integrity.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240402201123.2961909-2-paweldembicki@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>