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/rpc_link.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "link_layer.hpp"
+#include <vanetza/access/interface.hpp>
+#include <vanetza/rpc/asio_event_loop.hpp>
+#include <vanetza/rpc/asio_event_port.hpp>
+#include <vanetza/rpc/asio_stream.hpp>
+#include <vanetza/rpc/link_layer_client.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/program_options/options_description.hpp>
+#include <kj/async.h>
+
+class RpcLinkLayer : public LinkLayer
+{
+public:
+    /**
+     * Create RPC link layer
+     * \param io ASIO context
+     * \param socket TCP socket connected to RPC server
+     */
+    RpcLinkLayer(boost::asio::io_context& io, boost::asio::ip::tcp::socket socket);
+    ~RpcLinkLayer() noexcept;
+
+    void request(const vanetza::access::DataRequest&, std::unique_ptr<vanetza::ChunkPacket>) override;
+    void indicate(IndicationCallback) override;
+    void set_source_address(const vanetza::MacAddress&) override;
+
+    void radio_technology(const std::string&);
+    void enable_debug(bool);
+    static void add_options(boost::program_options::options_description&);
+
+private:
+    boost::asio::io_context& io_;
+    vanetza::rpc::AsioEventPort event_port_;
+    vanetza::rpc::AsioEventLoop event_loop_;
+    vanetza::rpc::AsioStream asio_stream_;
+    kj::WaitScope wait_scope_;
+    vanetza::rpc::LinkLayerClient client_;
+    IndicationCallback callback_;
+};