firewall: the firewall did not start properly on boot

https://dev.openwrt.org/ticket/17593

Signed-off-by: John Crispin <blogic@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42233 3c298f89-4303-0410-b956-a3cf2f4a3e73