Inject latency from a rule's action

[qdeslandes]

Allow a rule to inject latency on RX path by combining mark and TC qdiscs.

BPF cannot inject latency to packets by itself. Instead, we can rely on TC: bpfilter can mark matching packets, and a TC qdisc can inject latency based on the packet's mark. Marking packets is already supported by bpfilter.

• bpfilter must create and manage the qdisc: create/deleted depending on the rule(s)
• Add a new keyword in bfcli to inject latency on a rule