net: ethtool: Introduce ETHTOOL_LINK_MEDIUM_* values

In an effort to have a better representation of Ethernet ports,
introduce enumeration values representing the various ethernet Mediums.

This is part of the 802.3 naming convention, for example :

1000 Base T 4
 |    |   | |
 |    |   | \_ pairs (4)
 |    |   \___ Medium (T == Twisted Copper Pairs)
 |    \_______ Baseband transmission
 \____________ Speed

 Other example :

10000 Base K X 4
           | | \_ lanes (4)
           | \___ encoding (BaseX is 8b/10b while BaseR is 66b/64b)
           \_____ Medium (K is backplane ethernet)

In the case of representing a physical port, only the medium and number
of pairs should be relevant. One exception would be 1000BaseX, which is
currently also used as a medium in what appears to be any of 1000BaseSX,
1000BaseCX, 1000BaseLX, 1000BaseEX, 1000BaseBX10 and some other.

This was reflected in the mediums associated with the 1000BaseX linkmode.

These mediums are set in the net/ethtool/common.c lookup table that
maintains a list of all linkmodes with their number of pairs, medium,
encoding, speed and duplex.

One notable exception to this is 100BaseT Ethernet. It emcompasses 100BaseTX,
which is a 2-pairs protocol but also 100BaseT4, that will also work on 4-pairs
cables. As we don't make a disctinction between these,  the lookup table
contains 2 sets of pair numbers, indicating the min number of pairs for a
protocol to work and the "nominal" number of pairs as well.

Another set of exceptions are linkmodes such 100000baseLR4_ER4, where
the same link mode seems to represent 100GBaseLR4 and 100GBaseER4. The
macro __DEFINE_LINK_MODE_PARAMS_MEDIUMS is here used to populate the
.mediums bitfield with all appropriate mediums.

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260108080041.553250-3-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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