networkd: make network_load_one "public" and add a fuzzer for it

src/network/fuzz-network-parser.c

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "fuzz.h"
+#include "networkd-manager.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_(manager_freep) Manager *manager = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_(unlink_tempfilep) char network_config[] = "/tmp/fuzz-networkd.XXXXXX";
+
+        assert_se(fmkostemp_safe(network_config, "r+", &f) == 0);
+        if (size != 0)
+                assert_se(fwrite(data, size, 1, f) == 1);
+
+        rewind(f);
+        assert_se(manager_new(&manager) >= 0);
+        (void) network_load_one(manager, network_config);
+        return 0;
+}