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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,35 @@
+#pragma once
+#include <vanetza/access/access_category.hpp>
+#include <cstdint>
+
+namespace vanetza
+{
+namespace access
+{
+
+/**
+ * \brief map access category to PPPP for C-V2X
+ *
+ * Mapping is according to EN 303 613 V1.1.1 Table B.7
+ *
+ * \param ac access category from 802.11
+ * \return matching PPPP value
+ */
+constexpr std::uint8_t pppp_from_ac(AccessCategory ac)
+{
+    switch (ac) {
+        case AccessCategory::VO:
+            return 2;
+        case AccessCategory::VI:
+            return 4;
+        case AccessCategory::BE:
+            return 5;
+        case AccessCategory::BK:
+        default:
+            return 7;
+    }
+}
+
+} // namespace access
+} // namespace vanetza
+