qeth: l3 fix build error in ipv6 addr list handling

Adapt qeth l3 to:
commit c2e21293
(ipv6: convert addrconf list to hlist)
converted lst_next member of inet6_ifaddr struct to a hlist.

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