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/asio/cohda.hpp

@@ -0,0 +1,44 @@
+#ifndef COHDA_HPP_CCA3HKJO
+#define COHDA_HPP_CCA3HKJO
+
+#include <vanetza/asio/linklayer_endpoint.hpp>
+#include <boost/asio/basic_raw_socket.hpp>
+#include <linux/if_ether.h>
+#include <net/if.h>
+
+namespace vanetza
+{
+namespace asio
+{
+
+class cohda
+{
+    public:
+    typedef linklayer_endpoint<cohda> endpoint;
+    typedef boost::asio::basic_raw_socket<cohda> socket;
+
+    static cohda wave_raw()
+    {
+        return cohda("wave-raw", ETH_P_ALL);
+    }
+
+    explicit cohda() : m_protocol(ETH_P_ALL), m_ifidx(0) {}
+
+    int type() const { return SOCK_RAW; }
+    int family() const { return PF_PACKET; }
+    int protocol() const { return m_protocol; }
+    int interface_index() const { return m_ifidx; }
+
+    private:
+    explicit cohda(const char* if_name, int proto) :
+        m_protocol(proto), m_ifidx(if_nametoindex(if_name)) {}
+
+    int m_protocol; /*< ethernet protocol number */
+    int m_ifidx; /*< network interface card number */
+};
+
+} // namespace asio
+} // namespace vanetza
+
+#endif /* COHDA_HPP_CCA3HKJO */
+