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/geonet/common_header.hpp

@@ -0,0 +1,54 @@
+#ifndef COMMON_HEADER_HPP_SEFIWCT4
+#define COMMON_HEADER_HPP_SEFIWCT4
+
+#include <vanetza/common/bit_number.hpp>
+#include <vanetza/geonet/header_type.hpp>
+#include <vanetza/geonet/mib.hpp>
+#include <vanetza/geonet/position_vector.hpp>
+#include <vanetza/geonet/serialization.hpp>
+#include <vanetza/geonet/traffic_class.hpp>
+#include <cstdint>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+struct Area;
+struct DataRequest;
+struct ShbDataRequest;
+class LocationTable;
+
+enum class NextHeaderCommon
+{
+    Any = 0, BTP_A = 1, BTP_B = 2, IPv6 = 3
+};
+
+struct CommonHeader
+{
+public:
+    CommonHeader();
+    CommonHeader(const MIB&);
+    CommonHeader(const DataRequest&, const MIB&);
+    CommonHeader(const ShbDataRequest&, const MIB&);
+
+    static constexpr std::size_t length_bytes = 8;
+
+    NextHeaderCommon next_header; // 4 bit
+    BitNumber<unsigned, 4> reserved1;
+    HeaderType header_type;
+    TrafficClass traffic_class;
+    uint8_t flags; // Bit 0: itsGnIsMobile
+    uint16_t payload; // number of octets following whole GeoNet header
+    uint8_t maximum_hop_limit;
+    uint8_t reserved2;
+};
+
+void serialize(const CommonHeader&, OutputArchive&);
+void deserialize(CommonHeader&, InputArchive&);
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* COMMON_HEADER_HPP_SEFIWCT4 */
+