Cyphal/UDP: LinkLayerSniffer shall only accept frames from a specific NIC

The UDP tracer reports invalid transfer-ID errors as follows:

2023-09-01 23:54:02 1930786 DEB pycyphal.transport.redundant._tracer: RedundantTracer({(<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945704416784): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a4899010>, (<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945717383696): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a71d3b90>}): Processing RedundantCapture(timestamp=Timestamp(system_ns=1693601642728726000, monotonic_ns=993420910877439), inferior=UDPCapture(timestamp=Timestamp(system_ns=1693601642728726000, monotonic_ns=993420910877439), link_layer_packet=LinkLayerPacket(protocol=2, source=01005e001d55, destination=00248c4216fd, payload=4500003fb5a040001011e647c0a801c8ef001d55952a24a6002bcf0201043f8fffff551d3e000000000000000000008000003bfa010000000000569e7bb9a4)), iface_id=139945717383696, transfer_id_modulo=18446744073709551616)
2023-09-01 23:54:02 1930786 DEB pycyphal.transport.redundant._tracer: RedundantTracer({(<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945704416784): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a4899010>, (<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945717383696): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a71d3b90>}): BYPASS: UDPErrorTrace(timestamp=Timestamp(system_ns=1693601642728726000, monotonic_ns=993420910877439), error=<Error.UNEXPECTED_TRANSFER_ID: 2>)

Same but with manual line breaks:

2023-09-01 23:54:02 1930786 DEB pycyphal.transport.redundant._tracer:
    RedundantTracer({(<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945704416784): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a4899010>, (<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945717383696): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a71d3b90>}):
        Processing RedundantCapture(
            timestamp=Timestamp(system_ns=1693601642728726000, monotonic_ns=993420910877439),
                inferior=UDPCapture(
                    timestamp=Timestamp(system_ns=1693601642728726000, monotonic_ns=993420910877439),
                    link_layer_packet=LinkLayerPacket(
                        protocol=2,
                        source=01005e001d55,
                        destination=00248c4216fd,
                        payload=4500003fb5a040001011e647c0a801c8ef001d55952a24a6002bcf0201043f8fffff551d3e000000000000000000008000003bfa010000000000569e7bb9a4
                    )
                ),
                iface_id=139945717383696,
                transfer_id_modulo=18446744073709551616)

2023-09-01 23:54:02 1930786 DEB pycyphal.transport.redundant._tracer:
    RedundantTracer({(<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945704416784):
        <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a4899010>, (<class 'pycyphal.transport.udp._udp.UDPTransport'>, 139945717383696): <pycyphal.transport.udp._tracer.UDPTracer object at 0x7f47a71d3b90>}):
            BYPASS:
                UDPErrorTrace(
                    timestamp=Timestamp(system_ns=1693601642728726000,
                    monotonic_ns=993420910877439),
                    error=<Error.UNEXPECTED_TRANSFER_ID: 2>
                )

Reproducible with:

UAVCAN__UDP__IFACE="127.0.0.1 192.168.1.200" UAVCAN__NODE__ID=12345 y -vv mon 2>error.log

Not reproducible without interface redundancy.

Start with the reported reproduction command and trace how LinkLayerSniffer handles captures when interface redundancy is enabled. Inspect the UDP tracing and redundant transport paths involved in selecting an interface. Done means frames from other NICs are ignored and the invalid transfer-ID errors no longer occur in the reproduced redundant-interface case.