s390/qeth: convert to ETHTOOL_GLINKSETTINGS API

get_settings() is deprecated and lacks support for higher link
speeds, so implement get_link_ksettings() instead.

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Reviewed-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>