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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,59 @@
+#include "data_confirm.hpp"
+#include "data_request.hpp"
+
+namespace vanetza
+{
+namespace geonet
+{
+
+DataConfirm& operator ^=(DataConfirm& lhs, DataConfirm::ResultCode rhs)
+{
+    if (rhs != DataConfirm::ResultCode::Accepted) {
+        lhs.result_code = rhs;
+    }
+    return lhs;
+}
+
+DataConfirm::ResultCode validate_data_request(const DataRequest& req, const MIB& mib)
+{
+    DataConfirm::ResultCode result = DataConfirm::ResultCode::Rejected_Unspecified;
+
+    // TODO: traffic class validation
+    if (req.maximum_lifetime > mib.itsGnMaxPacketLifetime) {
+        result = DataConfirm::ResultCode::Rejected_Max_Lifetime;
+    } else if (req.repetition && req.repetition->interval < mib.itsGnMinPacketRepetitionInterval) {
+        result = DataConfirm::ResultCode::Rejected_Min_Repetition_Interval;
+    } else {
+        result = DataConfirm::ResultCode::Accepted;
+    }
+
+    return result;
+}
+
+DataConfirm::ResultCode validate_data_request(const DataRequestWithArea& req, const MIB& mib)
+{
+    if (area_size(req.destination) > mib.itsGnMaxGeoAreaSize) {
+        return DataConfirm::ResultCode::Rejected_Max_Geo_Area_Size;
+    } else {
+        return validate_data_request(static_cast<const DataRequest&>(req), mib);
+    }
+}
+
+DataConfirm::ResultCode validate_payload(const std::unique_ptr<DownPacket>& payload, const MIB& mib)
+{
+    DataConfirm::ResultCode result = DataConfirm::ResultCode::Rejected_Unspecified;
+
+    if (!payload) {
+        // leave code to unspecified
+    } else if (payload->size() > mib.itsGnMaxSduSize) {
+        result = DataConfirm::ResultCode::Rejected_Max_SDU_Size;
+    } else {
+        result = DataConfirm::ResultCode::Accepted;
+    }
+
+    return result;
+}
+
+} // namespace geonet
+} // namespace vanetza
+