Staging: batman-adv: Ommit storing struct device in sysfs functions

We actually do not need an extra struct device variable, therefore
replacing them with defines that directly get the bat_priv or
net_device. This further reduces the code size in bat_sysfs.c and
especially shortens some macros.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>