Staging: batman-adv: fix crash when new OGM is generated

If aggregation is not enabled the local translation table can grow
much bigger and expects to fill a full ethernet packet.

Reported-by: Sam Yeung <sam.cwyeung@gmail.com>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>