Verify performance gain/drop of packet filtering with nf_tables

[laeti-tia]

Firewalld developers claim that using a new nftables flowtables feature when activating packet filtering might improve performance, mainly in terms of throughput. They have published an article with some iperf3 performance benchmarks at https://firewalld.org/2023/05/nftables-flowtable

We should run our benchmarks to see if using this feature affects performance measured from high-end toolkit hosts.