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_rfill.c

@@ -0,0 +1,31 @@
+/*
+ * 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"
+
+asn_random_fill_result_t
+NULL_random_fill(const asn_TYPE_descriptor_t *td, void **sptr,
+                    const asn_encoding_constraints_t *constr,
+                    size_t max_length) {
+    asn_random_fill_result_t result_ok = {ARFILL_OK, 1};
+    asn_random_fill_result_t result_failed = {ARFILL_FAILED, 0};
+    asn_random_fill_result_t result_skipped = {ARFILL_SKIPPED, 0};
+    NULL_t *st = *sptr;
+
+    (void)td;
+    (void)constr;
+
+    if(max_length == 0) return result_skipped;
+
+    if(st == NULL) {
+        st = (NULL_t *)(*sptr = CALLOC(1, sizeof(*st)));
+        if(st == NULL) {
+            return result_failed;
+        }
+    }
+
+    return result_ok;
+}