s390/qeth: Fix vipa deletion

Change boolean parameter of function "qeth_l3_vipa_store" inside the
"qeth_l3_dev_vipa_del4_store" function from "true" to "false" because
"true" is used for adding a virtual ip address and "false" for deleting.

Fixes: 2390166a ("s390/qeth: clean up L3 sysfs code")

Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Signed-off-by: Thorsten Winkler <twinkler@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>