qeth: support ipv6 query arp cache for HiperSockets

Function qeth_l3_arp_query now queries for IPv6 addresses, too, if
QETH_QARP_WITH_IPV6 is passed as parameter to the ioctl. HiperSockets
and GuestLAN in HiperSockets mode provide corresponding entries.

Signed-off-by: Einar Lueck <elelueck@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>