glocalfile: Use MAXSYMLINKS when following symlinks

Currently, readlink() is used only 12 times when expanding symlinks.
However, kernel uses 40 for this purpose and it is defined as MAXSYMLINKS.
Use that constant if available, or 40. See:
https://github.com/torvalds/linux/include/linux/namei.h.

gio/glocalfile.c

@@ -1610,7 +1610,15 @@ expand_symlinks (const char *path,
         }
 
       num_recursions++;
-      if (num_recursions > 12)
+
+#ifdef MAXSYMLINKS
+      if (num_recursions > MAXSYMLINKS)
+#else
+      /* 40 is used in kernel sources currently:
+       * https://github.com/torvalds/linux/include/linux/namei.h
+       */
+      if (num_recursions > 40)
+#endif
         {
           g_free (target);
           return NULL;