Staging: batman-adv: fix rogue packets on shutdown

On module shutdown batman-adv would purge the internal packet
queue by sending all remaining packets which could confuse
other nodes. Now, the packets are silently discarded.

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>