Staging: batman-adv: Convert MAC_FMT to %pM

Remove the last uses of MAC_FMT

Signed-off-by: Joe Perches <joe@perches.com>
[sven.eckelmann@gmx.de: Adapted for current batman-adv version]
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>