batman-adv: fix bla compare function

The address and the VLAN VID may not be packed in the respective
structs. Fix this by comparing the elements individually.

Reported-by: Marek Lindner <lindner_marek@yahoo.de>
Reported-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>