net/mlx5e: Add ethtool extended link state

In case the interface was set up but cannot establish the link, ethtool
will print more information to help the user troubleshoot the state.

For example, no link due to missing cable:
$ ethtool eth1
...
Link detected: no (No cable)

Beside the general extended state, drivers can pass additional
information about the link state using the sub-state field. For example:

$ ethtool eth1
...
Link detected: no (Autoneg, No partner detected)

The extended state is available only for specific cases, in other cases
ethtool with print only "Link detected: no" as before

Signed-off-by: Moshe Tal <moshet@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>