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/proxy_header.hpp

@@ -0,0 +1,48 @@
+#ifndef PROXY_HEADER_HPP_JWTV3BDT
+#define PROXY_HEADER_HPP_JWTV3BDT
+
+#include <boost/range/iterator_range.hpp>
+#include <vanetza/access/access_category.hpp>
+#include <cstdint>
+
+namespace vanetza
+{
+
+#ifndef _MSC_VER
+// GCC and Clang support packed attribute
+#define PACKED_STRUCT(name, block) struct name { block } __attribute__((__packed__));
+#else
+// MSVC variant
+#define PACKED_STRUCT(name, block) \
+__pragma(pack(push, 1)) \
+struct name { block }; \
+__pragma(pack(pop))
+#endif
+
+PACKED_STRUCT(ProxyHeader,
+    /** offset in bytes to payload's first byte, counting from packet start */
+    uint16_t payload_offset;
+
+    /** length of payload in bytes */
+    uint32_t payload_size;
+
+    /** signal power in dBm, fixed point format 8.8 = trunc(double * 256) */
+    int16_t signal_power;
+
+    /** access category (transmission only) */
+    uint8_t access_category;
+)
+
+static_assert(sizeof(ProxyHeader) == 9, "ProxyHeader has invalid size");
+
+double get_signal_power(const ProxyHeader&);
+void set_signal_power(ProxyHeader&, double dbm);
+access::AccessCategory get_access_category(const ProxyHeader&);
+void set_access_category(ProxyHeader&, access::AccessCategory);
+boost::iterator_range<const uint8_t*> get_payload(const ProxyHeader&, std::size_t);
+void set_payload(ProxyHeader&, std::size_t);
+
+} // namespace vanetza
+
+#endif /* PROXY_HEADER_HPP_JWTV3BDT */
+