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FLASHING.md says how to take a newer version of the colleague's tree (copy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/tools/socktap/ethernet_device.hpp

@@ -0,0 +1,31 @@
+#ifndef ETHERNET_DEVICE_HPP_NEVC5DAY
+#define ETHERNET_DEVICE_HPP_NEVC5DAY
+
+#include <vanetza/net/mac_address.hpp>
+#include <boost/asio/generic/raw_protocol.hpp>
+#include <boost/asio/ip/address_v4.hpp>
+#include <string>
+
+class EthernetDevice
+{
+public:
+    using protocol = boost::asio::generic::raw_protocol;
+
+    EthernetDevice(const char* devname);
+    EthernetDevice(const EthernetDevice&) = delete;
+    EthernetDevice& operator=(const EthernetDevice&) = delete;
+    ~EthernetDevice();
+
+    protocol::endpoint endpoint(int family) const;
+    vanetza::MacAddress address() const;
+    boost::asio::ip::address_v4 ip() const;
+
+private:
+    int index() const;
+
+    int inet_socket_;
+    std::string interface_name_;
+};
+
+#endif /* ETHERNET_DEVICE_HPP_NEVC5DAY */
+