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/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 */
+