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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,134 @@
+#ifndef PACKET_BUFFER_HPP_U97KIBQC
+#define PACKET_BUFFER_HPP_U97KIBQC
+
+#include <vanetza/common/clock.hpp>
+#include <vanetza/geonet/packet.hpp>
+#include <vanetza/geonet/pdu.hpp>
+#include <vanetza/geonet/timestamp.hpp>
+#include <vanetza/net/mac_address.hpp>
+#include <functional>
+#include <list>
+#include <memory>
+
+namespace vanetza
+{
+namespace geonet
+{
+namespace packet_buffer
+{
+
+class Expiry
+{
+public:
+    Expiry(Clock::time_point now, Clock::duration lifetime);
+    bool is_expired(Clock::time_point now) const;
+    Clock::time_point buffered_since() const { return m_buffered_since; }
+    Clock::time_point expires_at() const { return m_expires_at; }
+
+private:
+    Clock::time_point m_buffered_since;
+    Clock::time_point m_expires_at;
+};
+
+class Data
+{
+public:
+    /**
+     * Length of packet data
+     * \return length in bytes
+     */
+    virtual std::size_t length() const = 0;
+
+    /**
+     * Reduce lifetime associated with data
+     * \param d reduce lifetime by given duration
+     * \return remaining lifetime (never negative)
+     */
+    virtual Clock::duration reduce_lifetime(Clock::duration d) = 0;
+
+    /**
+     * Flush data
+     * \note length() and lifetime() should not be called afterwards!
+     */
+    virtual void flush() = 0;
+
+    virtual ~Data() {}
+};
+
+} // namespace packet_buffer
+
+
+/**
+ * PacketBuffer with bounded capacity, packet expiry and head-drop
+ */
+class PacketBuffer
+{
+public:
+    typedef std::unique_ptr<packet_buffer::Data> data_ptr;
+
+    /**
+     * Create PacketBuffer with given capacity
+     * \param capacity Buffer can store this many bytes
+     */
+    PacketBuffer(std::size_t capacity);
+
+    /**
+     * Push one packet into buffer
+     * \param packet Packet data
+     * \param t Current time
+     * \return true if packet has been pushed successfully
+     */
+    bool push(data_ptr packet, Clock::time_point t);
+
+    /**
+     * Flush packets from buffer. Expired packets are dropped.
+     * \note Some packets might remain in buffer (re-added during flushing)
+     * \param t Current time
+     */
+    void flush(Clock::time_point t);
+
+private:
+    typedef packet_buffer::Expiry expiry_type;
+    typedef std::tuple<expiry_type, data_ptr> node_type;
+
+    std::size_t free() const { return m_capacity - m_stored; }
+    std::size_t capacity() const { return m_capacity; }
+
+    /**
+     * Push one new element into buffer list
+     * \note capacity is not checked by this method, has to be done manually
+     * \param expiry Expiry data
+     * \param packet Packet data
+     */
+    void push(expiry_type&& expiry, data_ptr packet);
+
+    /**
+     * Drop current head element
+     * \return true if head element was dropped
+     */
+    bool drop_head();
+
+    /**
+     * Drop all packets with expired timestamp
+     * \param t current time
+     */
+    void drop_expired(Clock::time_point t);
+
+    /**
+     * Drop as many packets as required to store given number of bytes.
+     * Packets at the head of the list are dropped first.
+     * \param bytes require #bytes free capacity
+     * \return true if there is enough capacity left for #bytes
+     */
+    bool drop(std::size_t bytes);
+
+    std::list<node_type> m_nodes;
+    std::size_t m_capacity;
+    std::size_t m_stored;
+};
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* PACKET_BUFFER_HPP_U97KIBQC */
+