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FLASHING.md says how to take a newer version of the colleague's tree (copy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/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 */
+