Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/tools/socktap/autotalks_link.hpp

@@ -0,0 +1,34 @@
+#ifndef AUTOTALKS_LINK_HPP_
+#define AUTOTALKS_LINK_HPP_
+
+#include "raw_socket_link.hpp"
+#include "atlk/v2x_service.h"
+#include <iostream>
+
+class AutotalksLink : public LinkLayer
+{
+public:
+    /*
+     * Constructor used for device and thread initialization.
+     */
+    AutotalksLink(boost::asio::io_context&);
+
+    /*
+     * Destructor used for deinitialization.
+     */
+    ~AutotalksLink(void);
+    void request(const vanetza::access::DataRequest&, std::unique_ptr<vanetza::ChunkPacket>) override;
+    void indicate(IndicationCallback callback) override;
+    void data_received(uint8_t*, uint16_t, v2x_receive_params_t);
+
+private:
+    static constexpr std::size_t layers_ = num_osi_layers(vanetza::OsiLayer::Physical, vanetza::OsiLayer::Application);
+    IndicationCallback callback_;
+    std::array<vanetza::ByteBuffer, layers_> buffers_;
+    boost::asio::io_context& io_;
+};
+
+
+
+#endif /* AUTOTALKS_LINK_HPP_ */
+