multiple hooks at the same callout point
We have a generic issue when more than one hook uses a packet processing callout point:
- even when a hook does not modify the handle status it should check it to for instance not perform action when the status was set to DROP by a preceding hook.
- for hooks doing packing or unpacking there is another case: the SKIP status.
Note the doc should be updated to warn hook writers to not forget to check the handle status (same than to check packets are not null before deferring them).