AA: kernel: fix CVE-2013-1763

Backport of r36607.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/branches/attitude_adjustment@36608 3c298f89-4303-0410-b956-a3cf2f4a3e73
Merge branch 'master' into scooreggione