Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/tools/socktap/ethernet_device.hpp

@@ -0,0 +1,31 @@
+#ifndef ETHERNET_DEVICE_HPP_NEVC5DAY
+#define ETHERNET_DEVICE_HPP_NEVC5DAY
+
+#include <vanetza/net/mac_address.hpp>
+#include <boost/asio/generic/raw_protocol.hpp>
+#include <boost/asio/ip/address_v4.hpp>
+#include <string>
+
+class EthernetDevice
+{
+public:
+    using protocol = boost::asio::generic::raw_protocol;
+
+    EthernetDevice(const char* devname);
+    EthernetDevice(const EthernetDevice&) = delete;
+    EthernetDevice& operator=(const EthernetDevice&) = delete;
+    ~EthernetDevice();
+
+    protocol::endpoint endpoint(int family) const;
+    vanetza::MacAddress address() const;
+    boost::asio::ip::address_v4 ip() const;
+
+private:
+    int index() const;
+
+    int inet_socket_;
+    std::string interface_name_;
+};
+
+#endif /* ETHERNET_DEVICE_HPP_NEVC5DAY */
+