batman-adv: a multiline comment should precede the variable it is describing

This comment has been wrongly put after the variable it refers to and was also bad indented

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Acked-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Sven Eckelmann <sven@narfation.org>