linux: add support for ethtool GLINKSETTINGS

linux: add support for ethtool GLINKSETTINGS

With a recent enough kernel, one can use GLINKSETTINGS instead of
GSET. This is needed to overcome the limitation on the number of
supported/advertising modes supported by GSET (which is a fixed-length
bitset). We use the same kind of compatibility structure than for
ethtool.

Also, update the list of supported MAU types to support higher speed
interfaces. Unfortunately, while Linux reports the exact
advertised/supported modes, the operational mode of the interface is
only reported with its speed and its kind (copper, fiber, ...). When
this is fiber, we don't know if this is MMF or SMF or the supported
distance. Therefore, we use our best guess (this was already the case,
nothing new here).