s390/qeth: query IPv6 IPA support on HiperSockets

HiperSocket devices don't need the full IPv6 initialization, but we
should still query the supported assists for logging purposes.

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