When reading a vdev label skip libzfs_core_init()

There's no need to call libzfs_core_init() when `zdb -l` is used to
read a vdev label.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: tiehexue <[email protected]>
Closes #18606

cmd/zdb/zdb.c

@@ -10230,7 +10230,7 @@ main(int argc, char **argv)
 	 * Automate cachefile
 	 */
 	if (!spa_config_path_env && !config_path_console && target &&
-	    libzfs_core_init() == 0) {
+	    !dump_opt['l'] && libzfs_core_init() == 0) {
 		char *pname = strdup(target);
 		const char *value;
 		nvlist_t *pnvl = NULL;