Staging: batman-adv: Create batman_if only on register event

We try to get all events for all net_devices to be able to add special
sysfs folders for the batman-adv configuration. This also includes such
events like NETDEV_POST_INIT which has no valid kobject according to
v2.6.32-rc3-13-g7ffbe3f. This would create an oops in that situation.

It is enough to create the batman_if only on NETDEV_REGISTER events
because we will also receive those events for devices which already
existed when we registered the notifier call.

Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>