s390/qeth: query IPv6 assists during hardsetup

For new functionality, the L2 subdriver will start using IPv6 assists.
So move the query from the L3 subdriver into the common setup path.

Signed-off-by: Kittipon Meesompop <kmeesomp@linux.vnet.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>