Drop experimental and ip6tables config (#4173)

The ip6tables configuration is now enabled by default since Docker 27
(see https://github.com/moby/moby/pull/47747). The experimental config
got introduced with the ip6tables flag in #2051. There is no other
experimental feature used from what I am aware of, so lets remove the
experimental flag as well.

buildroot-external/rootfs-overlay/etc/docker/daemon.json

@@ -1,8 +1,6 @@
 {
     "storage-driver": "overlay2",
     "log-driver": "journald",
-    "experimental": true,
-    "ip6tables": true,
     "log-opts": {
         "tag": "{{.Name}}"
     },