staging: batman-adv: Use linux/etherdevice.h address helper functions

Replace custom ethernet address check functions by calls to the helpers
in linux/etherdevice.h

In one case where the address was tested for broadcast and multicast
address, the broadcast address check can be omitted as broadcast is also
a multicast address.

The patch is only compile-tested.

Cc: Marek Lindner <lindner_marek@yahoo.de>
Cc: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>