fuzz: limit the interface definition input size to 64K

To avoid timeouts with larger inputs.

Resolves: #29856

src/fuzz/fuzz-varlink-idl.c

@@ -14,6 +14,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_free_ char *str = NULL, *dump = NULL;
         int r;
 
+        if (outside_size_range(size, 0, 64 * 1024))
+                return 0;
+
         fuzz_setup_logging();
 
         assert_se(str = memdup_suffix0(data, size));