kernel: improve ipv4 netfilter optimization patch

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

Backport of r42045

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42049 3c298f89-4303-0410-b956-a3cf2f4a3e73