tcp_scalable: Update malformed & dead url

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_scalable.c

 /* Tom Kelly's Scalable TCP
  *
- * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/
+ * See http://www.deneholme.net/tom/scalable/
  *
  * John Heffner <jheffner@sc.edu>
  */