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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,35 @@
+#ifndef BUFFER_PACKET_HPP_QYLSJSX5
+#define BUFFER_PACKET_HPP_QYLSJSX5
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/net/osi_layer.hpp>
+#include <cstddef>
+#include <map>
+
+namespace vanetza
+{
+
+class BufferPacket
+{
+public:
+    typedef std::map<OsiLayer, ByteBuffer> map_t;
+    BufferPacket();
+    void swap(OsiLayer layer, ByteBuffer&);
+    const ByteBuffer& operator[](OsiLayer layer) const;
+    ByteBuffer& operator[](OsiLayer layer) { return mBuffers[layer]; }
+    std::size_t size() const;
+    void clear();
+
+    map_t::iterator begin() { return mBuffers.begin(); }
+    map_t::iterator end() { return mBuffers.end(); }
+    map_t::const_iterator begin() const { return mBuffers.begin(); }
+    map_t::const_iterator end() const { return mBuffers.end(); }
+
+private:
+    map_t mBuffers;
+};
+
+} // namespace vanetza
+
+#endif /* BUFFER_PACKET_HPP_QYLSJSX5 */
+