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FLASHING.md says how to take a newer version of the colleague's tree (copy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/raw_socket_link.hpp

@@ -0,0 +1,38 @@
+#ifndef RAW_SOCKET_LINK_HPP_VUXH507U
+#define RAW_SOCKET_LINK_HPP_VUXH507U
+
+#include "link_layer.hpp"
+#include <vanetza/access/interface.hpp>
+#include <vanetza/net/ethernet_header.hpp>
+#include <boost/asio/generic/raw_protocol.hpp>
+#include <boost/optional/optional.hpp>
+#include <array>
+#include <functional>
+
+class RawSocketLink : public LinkLayer
+{
+public:
+    RawSocketLink(boost::asio::generic::raw_protocol::socket&&);
+    void request(const vanetza::access::DataRequest&, std::unique_ptr<vanetza::ChunkPacket>) override;
+    void indicate(IndicationCallback) override;
+
+protected:
+    std::size_t transmit(std::unique_ptr<vanetza::ChunkPacket>);
+    virtual boost::optional<vanetza::EthernetHeader> parse_ethernet_header(vanetza::CohesivePacket&) const;
+
+private:
+    void do_receive();
+    void on_read(const boost::system::error_code&, std::size_t);
+    void pass_up(vanetza::CohesivePacket&&);
+
+    static constexpr std::size_t layers_ = num_osi_layers(vanetza::OsiLayer::Physical, vanetza::OsiLayer::Application);
+
+    boost::asio::generic::raw_protocol::socket socket_;
+    std::array<vanetza::ByteBuffer, layers_> buffers_;
+    IndicationCallback callback_;
+    vanetza::ByteBuffer receive_buffer_;
+    boost::asio::generic::raw_protocol::endpoint receive_endpoint_;
+};
+
+#endif /* RAW_SOCKET_LINK_HPP_VUXH507U */
+