Report the interface ID used to capture pcapng files

[emarch06]

• On pcapng files, you can have several capture interfaces. We report this information to be able to use it on another classes
  I don't think adding a unit test for this is worth it, since We just report a field to the upper layer that is already parsed.

Note: It's my first contribution to scapy. Let me know if I missed something :-)

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests (using cd test && ./run_tests or tox)
• If the PR is still not finished, please create a Draft Pull Request

fixes #4731

[gpotter2]

Hi, thanks for the PR.
I don't really understand where you're getting those IDs from. Packets already have the interface they're sniffed on as parameter, isn't that enough?
Thanks

[emarch06]

Hi @gpotter2,

we'd like to use the interface ID of the pcapng in a wireshark-way

In the python code, it would be like this:

sniff(prn=self._scapy_callback, ....

def _scapy_callback(self, packet):
    eth_message.interface_id = packet.intid

In pcapng,
interface name is parsed from Interface Description Block (method: _read_block_idb)

Then, parsing the packets of the pcapng,
The Interface ID value refers to a particular Interface Description Block by referencing its implicit zero-indexed IDB position in the current section.
I.e. the first IDB defined in a section has Interface ID 0x00000000, the second one has 0x00000001, and so on.

we didn't find a way to get this information from a Packet instance.
Maybe I'm wrong and this patch is useless. In this case, could you explain me how to do this?

Thanks in advance