ethtool: Extend cable testing interface with result source information

ethtool: Extend cable testing interface with result source information

Extend the ethtool netlink cable testing interface by adding support for
specifying the source of cable testing results. This allows users to
differentiate between results obtained through different diagnostic
methods.

For example, some TI 10BaseT1L PHYs provide two variants of cable
diagnostics: Time Domain Reflectometry (TDR) and Active Link Cable
Diagnostic (ALCD). By introducing `ETHTOOL_A_CABLE_RESULT_SRC` and
`ETHTOOL_A_CABLE_FAULT_LENGTH_SRC` attributes, this update enables
drivers to indicate whether the result was derived from TDR or ALCD,
improving the clarity and utility of diagnostic information.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20240822120703.1393130-2-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>