s390/qeth: replace qeth_l3_get_addr_buffer()

The remaining usage effectively is a kmemdup() of the query object.
By not wrapping it, some of the callers can now use GFP_KERNEL for the
allocation.

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