Documentation/fs/9p: Expand goo.gl link

The goo.gl URL shortener is deprecated and is due to stop
expanding existing links in 2025.

The old goo.gl link in the 9p docs doesn't work anyway,
replace it by a kernel.org link suggested by Randy instead.
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240725180041.80862-1-linux@treblig.org

Documentation/filesystems/9p.rst

@@ -31,7 +31,7 @@ Other applications are described in the following papers:
 	* PROSE I/O: Using 9p to enable Application Partitions
 	  http://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf
 	* VirtFS: A Virtualization Aware File System pass-through
-	  http://goo.gl/3WPDg
+	  https://kernel.org/doc/ols/2010/ols2010-pages-109-120.pdf
 
 Usage
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