Documentation/admin-guide: update URL of LKML information link

Information regarding linux-kernel mailing list is no longer hosted on tux.org
Update the link to point to the one available at kernel.org
Signed-off-by: Ramunas Geciauskas <kernel@geciauskas.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/reporting-bugs.rst

@@ -67,7 +67,7 @@ If you can't figure out which subsystem caused the issue, you should file
 a bug in kernel.org bugzilla and send email to
 linux-kernel@vger.kernel.org, referencing the bugzilla URL.  (For more
 information on the linux-kernel mailing list see
-http://www.tux.org/lkml/).
+http://vger.kernel.org/lkml/).
 
 
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