base-files: enable option to skip the netfilter "filter" table for established connection packets by default

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

Backport of r42048

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42051 3c298f89-4303-0410-b956-a3cf2f4a3e73