Staging: batman-adv: Don't increment stats of foreign device

The receive hook for batman-adv ethernet frames tried to get the last
device which processed the skb before us. It only used that information
to update the rx_bytes and rx_packets stat of that foreign device which
already has updated it using its own receive functions.

Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>