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/asn1/support/NULL_print.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2017 Lev Walkin <vlm@lionet.info>.
+ * All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#include "asn_internal.h"
+#include "NULL.h"
+
+int
+NULL_print(const asn_TYPE_descriptor_t *td, const void *sptr, int ilevel,
+           asn_app_consume_bytes_f *cb, void *app_key) {
+    (void)td;  /* Unused argument */
+    (void)ilevel;  /* Unused argument */
+
+    if(sptr) {
+        return (cb("<present>", 9, app_key) < 0) ? -1 : 0;
+    } else {
+        return (cb("<absent>", 8, app_key) < 0) ? -1 : 0;
+    }
+}