Comment 2 for bug 1664294

@ Cedric Brandily,
Thank you for pointing out the problem in the Netlink feature.
My planning to improve the Netlink feature as good as possible, and also make the conntrack configurable (we can switch between conntrack-tools and Netlink), make conntrack-tools as default.
In my opinion, keeping the netlink_lib module is necessary because it can be a good reference of improving conntrack performance