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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,57 @@
+#include "proxy_header.hpp"
+#include <vanetza/common/byte_order.hpp>
+#include <cassert>
+
+namespace vanetza
+{
+
+double get_signal_power(const ProxyHeader& header)
+{
+    double power = ntoh(header.signal_power);
+    power /= 256.0;
+    return power;
+}
+
+void set_signal_power(ProxyHeader& header, double dbm)
+{
+    auto power = static_cast<decltype(ProxyHeader::signal_power)>(dbm * 256.0);
+    header.signal_power = hton(power);
+}
+
+access::AccessCategory get_access_category(const ProxyHeader& header)
+{
+    return static_cast<access::AccessCategory>(header.access_category & 0x07);
+}
+
+void set_access_category(ProxyHeader& header, access::AccessCategory ac)
+{
+    header.access_category = static_cast<uint8_t>(ac);
+}
+
+boost::iterator_range<const uint8_t*> get_payload(const ProxyHeader& header, std::size_t size)
+{
+    const auto payload_offset = ntoh(header.payload_offset);
+    const auto payload_size = ntoh(header.payload_size);
+
+    assert(size >= payload_offset + payload_size);
+    assert(payload_offset >= sizeof(ProxyHeader));
+
+    const uint8_t* begin = reinterpret_cast<const uint8_t*>(&header);
+    const uint8_t* end = begin;
+
+    if (size >= payload_offset + payload_size) {
+        begin += payload_offset;
+        end = begin + payload_size;
+    }
+
+    return boost::make_iterator_range(begin, end);
+}
+
+void set_payload(ProxyHeader& header, std::size_t size)
+{
+    header.payload_offset = hton<decltype(header.payload_offset)>(sizeof(ProxyHeader));
+    header.payload_size = hton<decltype(header.payload_size)>(size);
+}
+
+} // namespace vanetza
+