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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,62 @@
+#include "next_hop.hpp"
+
+namespace vanetza
+{
+namespace geonet
+{
+
+NextHop::NextHop() : m_state(State::Discarded)
+{
+}
+
+bool NextHop::discarded() const
+{
+    return m_state == State::Discarded;
+}
+
+bool NextHop::buffered() const
+{
+    return m_state == State::Buffered;
+}
+
+bool NextHop::valid() const
+{
+    return m_state == State::Valid;
+}
+
+const MacAddress& NextHop::mac() const
+{
+    return m_destination;
+}
+
+bool NextHop::process() &&
+{
+    if (valid()) {
+        PendingPacket<GbcPdu>(std::move(m_packet), m_destination).process();
+        m_state = State::Discarded;
+        return true;
+    } else {
+        return false;
+    }
+}
+
+void NextHop::transmit(Packet&& packet, const MacAddress& destination)
+{
+    m_state = NextHop::State::Valid;
+    m_packet = std::move(packet);
+    m_destination = destination;
+}
+
+void NextHop::discard()
+{
+    m_state = NextHop::State::Discarded;
+}
+
+void NextHop::buffer()
+{
+    m_state = NextHop::State::Buffered;
+}
+
+} // namespace geonet
+} // namespace vanetza
+