[Cake] issue with Cake and bpf filter

[Toke Høiland-Jørgensen]

>> The next simplest fix is to ignore the flow ID override unless we're
>> in "flows" mode. We can then make valid assumptions about what should
>> go into the host tables.
>>
>> The *right* fix, if we want to maximise functionality, would be to
>> pass the result struct by reference into cake_hash(), where it can
>> override the *host* IDs (not the flow ID). Users can then choose
>> between using the override as a flow ID (by setting "hosts" mode
>> instead of "flows"), or retaining the default host-isolation semantics
>> with a revised definition of "host".
>
> Ah, making it possible to override both host and flow mode is a great
> idea! I guess we could use the major/minor distinction in the class to
> steer this. I'll see if I can't integrate this.

So, I implemented this; in the latest commit on github it is again
possible to override the flow hashing by setting the class ID with a TC
filter; and the host hash can be overridden by setting the major number
of the class ID. In my testing the hangs from before are gone, but if
anyone else wants to test, please do!

I'll write up a description of the filter overrides in the man page, and
submit the change upstream as well...

-Toke