Kobject: convert drivers/net/iseries_veth.c to use kobject_init/add_ng()

This converts the code to use the new kobject functions, cleaning up the
logic in doing so.

Cc: Kyle A. Lucke <klucke@us.ibm.com>
Cc: David Gibson <dwg@au1.ibm.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>