batman-adv: broadcast primary OGM on all active hard-interfaces

The primary interface OGM has to be broadcasted on all hard-interfaces
even if the primary interface is not the first interface (if_num = 0).
Therefore the code has to compare the originating interface with the
primary interface instead of checking the if_num.

Reported-by: Linus Luessing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>