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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,52 @@
+#ifndef DATA_CONFIRM_HPP_Z1WCMN8T
+#define DATA_CONFIRM_HPP_Z1WCMN8T
+
+#include <vanetza/geonet/mib.hpp>
+#include <vanetza/geonet/packet.hpp>
+#include <memory>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+struct DataRequest;
+struct DataRequestWithArea;
+
+struct DataConfirm
+{
+    enum class ResultCode {
+        Accepted,
+        Rejected_Max_SDU_Size,
+        Rejected_Max_Lifetime,
+        Rejected_Min_Repetition_Interval,
+        Rejected_Unsupported_Traffic_Class,
+        Rejected_Max_Geo_Area_Size,
+        Rejected_Unspecified
+    };
+
+    DataConfirm() : result_code(ResultCode::Accepted) {}
+    DataConfirm(ResultCode code) : result_code(code) {}
+    bool accepted() const { return result_code == ResultCode::Accepted; }
+    bool rejected() const { return !accepted(); }
+    ResultCode result_code;
+};
+
+/**
+ * XOR result code with DataConfirm's result code.
+ * Replaces result code of DataConfirm only if new code is an error code.
+ * \param lhs Operate on this DataConfirm
+ * \param rhs XOR this ResultCode with lhs
+ * \return reference to modified DataConfirm
+ */
+DataConfirm& operator ^=(DataConfirm& lhs, DataConfirm::ResultCode rhs);
+
+DataConfirm::ResultCode validate_data_request(const DataRequest&, const MIB&);
+DataConfirm::ResultCode validate_data_request(const DataRequestWithArea&, const MIB&);
+DataConfirm::ResultCode validate_payload(const std::unique_ptr<DownPacket>&, const MIB&);
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* DATA_CONFIRM_HPP_Z1WCMN8T */
+