s390/qeth: use LINK_MODE_* to report the link characteristics

LINK_MODE_* replaces the u32-limited SUPPORTED_* / ENABLED_*
definitions.

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>