Add support for latency (enhancement)

[giusepperagusa]

When simulating WAN links it would be useful to be able to add a fixed latency along the lines of:

tc qdisc add dev eth0 root netem delay 100ms

[LeOSW42]

I'm exactly needing that to simulate Antarctica bad network conditions: 100kbps up/down and 500ms latency.

[RussellBradley]

+1 for packets latency/delay.

[magnific0]

tc does latency, so it could be integrated in wondershaper. I'm open to PRs, but it should be separately configurable from limiting, which is the primary use case.

[lionkunonly]

@magnific0 The netem command is classless, Do you know how to set the latency in tc class? I can not find the corresponding documents for it now.