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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,44 @@
+#include "buffer_packet.hpp"
+
+namespace vanetza
+{
+
+BufferPacket::BufferPacket()
+{
+}
+
+void BufferPacket::swap(OsiLayer layer, ByteBuffer& replacement)
+{
+    ByteBuffer& stored = mBuffers[layer];
+    stored.swap(replacement);
+}
+
+const ByteBuffer& BufferPacket::operator[](OsiLayer layer) const
+{
+    auto match = mBuffers.find(layer);
+    if (match == mBuffers.end()) {
+        static const ByteBuffer scEmptyBuffer;
+        return scEmptyBuffer;
+    } else {
+        return match->second;
+    }
+}
+
+std::size_t BufferPacket::size() const
+{
+    std::size_t packet_size = 0;
+    for (const auto& it : *this) {
+        packet_size += it.second.size();
+    }
+    return packet_size;
+}
+
+void BufferPacket::clear()
+{
+    for (auto& it : mBuffers) {
+        it.second.clear();
+    }
+}
+
+} // namespace vanetza
+