batman-adv: only drop packets of known wifi clients

batman-adv: only drop packets of known wifi clients

bug introduced with e2c37c12b075f4be74940fd287b388c19e0a6a9f

If the source or destination mac address of an ethernet packet
could not be found in the translation table the packet was
dropped if AP isolation was turned on. This behavior would
make it impossible to send broadcast packets over the mesh as
the broadcast address will never enter the translation table.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Acked-by: Antonio Quartulli <ordex@autistici.org>