Allow TrafficGetFilterRequest to get ingress or egress filters

[azdle]

I'm using this library to make sure there aren't any other bpf programs bound to a qdisc before deleting it. Bpf programs show up as ingress and egress traffic control filters which it seems this library isn't currently able to query.

These changes are based on what bpftool does, copying the already existing root (just above these changes) but setting ingress and egress. And I'm just noticing that it ended up being an exact copy of functions from TrafficFilterNewRequest

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These options are the equivalent of:

tc filter show dev DEV ingress

and

tc filter show dev DEV egress