kernel: fix crash in act_connmark in 3.9 and 3.10 (fixes #13916, #13876)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37493 3c298f89-4303-0410-b956-a3cf2f4a3e73