Staging: batman-adv: stop persistent warnings if a device is deactivated.

Without this change we spam the kernel log on every packet received on
any other interface when an interface has been added, but is not yet
active, ie UP.

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>