Staging: batman-adv: fix own mac address detection

Earlier batman-adv versions would only create a batman_if struct after
a corresponding interface had been activated by a user. Now each
existing system interface has a batman_if struct and has to be checked
by verifying the IF_ACTIVE flag.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>