Staging: batman-adv: check kmalloc() return value

kmalloc() may fail, if so drop current packet.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
[sven.eckelmann@gmx.de: Removed new introduced deadlock]
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>