Staging: batman-adv: Always receive when discarding.

It does not matter if the interface is to be activated or not, we must
read the packet in order that it be discarded.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>