batman-adv: reorder batadv_iv_flags

The vis flag is not needed anymore, and since we do a compat bump we
can start with the first bit again

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>