net: atheros: atl2: use new api ethtool_{get|set}_link_ksettings

The ethtool api {get|set}_settings is deprecated.
We move this driver to new api {get|set}_link_ksettings.

The previous implementation of set_settings was modifying
the value of advertising, but with the new API, it's not
possible. The structure ethtool_link_ksettings is defined
as const.

Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>