After some analysis, stateful filtering is only necessary in tailnets
that use `autogroup:danger-all` in `src` in ACLs. And in those cases
users explicitly specify that hosts outside of the tailnet should be
able to reach their nodes. To fix local DNS breakage in containers, we
disable stateful filtering by default.
Updates #12108
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>