docs: rcu: Replace multiple dead OLS links in RTFP.txt

This patch updates several dead OLS links in RTFP.txt, replacing them
with working copies hosted on kernel.org.

Originally posted as part of a 2-patch series, this is now being sent
as a standalone v4 patch to avoid confusion.

Signed-off-by: Nikil Paul S <snikilpaul@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: Nikil-D-Gr8

Documentation/RCU/RTFP.txt

@@ -641,7 +641,7 @@ Orran Krieger and Rusty Russell and Dipankar Sarma and Maneesh Soni"
 ,Month="July"
 ,Year="2001"
 ,note="Available:
-\url{http://www.linuxsymposium.org/2001/abstracts/readcopy.php}
+\url{https://kernel.org/doc/ols/2001/read-copy.pdf}
 \url{http://www.rdrop.com/users/paulmck/RCU/rclock_OLS.2001.05.01c.pdf}
 [Viewed June 23, 2004]"
 ,annotation={
@@ -1480,7 +1480,7 @@ Suparna Bhattacharya"
 ,Year="2006"
 ,pages="v2 123-138"
 ,note="Available:
-\url{http://www.linuxsymposium.org/2006/view_abstract.php?content_key=184}
+\url{https://kernel.org/doc/ols/2006/ols2006v2-pages-131-146.pdf}
 \url{http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf}
 [Viewed January 1, 2007]"
 ,annotation={
@@ -1511,7 +1511,7 @@ Canis Rufus and Zoicon5 and Anome and Hal Eisen"
 ,Year="2006"
 ,pages="v2 249-254"
 ,note="Available:
-\url{http://www.linuxsymposium.org/2006/view_abstract.php?content_key=184}
+\url{https://kernel.org/doc/ols/2006/ols2006v2-pages-249-262.pdf}
 [Viewed January 11, 2009]"
 ,annotation={
 	Uses RCU-protected radix tree for a lockless page cache.