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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,31 @@
+#include "channel_load.hpp"
+
+namespace vanetza
+{
+namespace dcc
+{
+
+ChannelLoad::ChannelLoad(const UnitInterval& interval) :
+    UnitInterval(interval)
+{
+}
+
+ChannelLoad::ChannelLoad(unsigned probes_busy, unsigned probes_total) :
+    UnitInterval(create_from_probes(probes_busy, probes_total))
+{
+}
+
+UnitInterval ChannelLoad::create_from_probes(unsigned probes_busy, unsigned probes_total)
+{
+    double fraction = 0.0;
+    if (probes_total != 0) {
+        fraction = probes_busy;
+        fraction /= probes_total;
+    }
+
+    return UnitInterval(fraction);
+}
+
+} // namespace dcc
+} // namespace vanetza
+