tar: use nlink_t for link counts

* src/create.c (struct link): nlink is now of type nlink_t, not size_t.

src/create.c

@@ -30,7 +30,7 @@ struct link
   {
     dev_t dev;
     ino_t ino;
-    size_t nlink;
+    nlink_t nlink;
     char name[1];
   };