Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/geonet/packet_buffer.cpp

@@ -0,0 +1,94 @@
+#include "packet_buffer.hpp"
+#include "basic_header.hpp"
+
+namespace vanetza
+{
+namespace geonet
+{
+namespace packet_buffer
+{
+
+Expiry::Expiry(Clock::time_point now, Clock::duration lifetime) :
+    m_buffered_since(now), m_expires_at(now)
+{
+    m_expires_at += lifetime;
+}
+
+bool Expiry::is_expired(Clock::time_point now) const
+{
+    return (m_expires_at < now);
+}
+
+} // namespace packet_buffer
+
+
+PacketBuffer::PacketBuffer(std::size_t capacity) :
+    m_capacity(capacity), m_stored(0)
+{
+}
+
+bool PacketBuffer::push(data_ptr data, Clock::time_point now)
+{
+    assert(data);
+    bool pushed = false;
+    drop_expired(now);
+    if (drop(data->length())) {
+        m_stored += data->length();
+        m_nodes.push_back(std::make_tuple(
+                    expiry_type(now, data->reduce_lifetime(Clock::duration::zero())),
+                    std::move(data)
+                ));
+        pushed = true;
+    }
+    return pushed;
+}
+
+void PacketBuffer::flush(Clock::time_point now)
+{
+    decltype(m_nodes) nodes;
+    std::swap(m_nodes, nodes);
+    m_stored = 0;
+
+    for (auto& node : nodes) {
+        const auto& expiry = std::get<0>(node);
+        if (!expiry.is_expired(now)) {
+            auto& data = std::get<1>(node);
+            const auto queuing_time = now - expiry.buffered_since();
+            data->reduce_lifetime(queuing_time);
+            data->flush();
+        }
+    }
+}
+
+bool PacketBuffer::drop_head()
+{
+    bool dropped = !m_nodes.empty();
+    if (dropped) {
+        m_stored -= std::get<1>(m_nodes.front())->length();
+        m_nodes.pop_front();
+    }
+    return dropped;
+}
+
+void PacketBuffer::drop_expired(Clock::time_point now)
+{
+    std::list<decltype(m_nodes)::iterator> expired;
+    for (auto it = m_nodes.begin(), end = m_nodes.end(); it != end;) {
+        if (std::get<0>(*it).is_expired(now)) {
+            m_stored -= std::get<1>(*it)->length();
+            it = m_nodes.erase(it);
+        } else {
+            ++it;
+        }
+    }
+}
+
+bool PacketBuffer::drop(std::size_t bytes)
+{
+    while (free() < bytes && drop_head()) {}
+    return free() >= bytes;
+}
+
+} // namespace geonet
+} // namespace vanetza
+