[PATCH v3 0/6] relay infrastructure

[Johannes Berg]

As promised yesterday, here's v3. Not really any changes except
in the basic infrastructure (where I added the DropFrames layer
as well), but it composes nicer now:

    with HwsimRelay(...) as relay, \
    with Layer1(relay, ...) as l1, \
    with Layer2(l1, ...) as l2:
        ...

johannes