[DCCP]: Update documentation references.

Updates the references to spec documents throughout the code, taking into
account that

* the DCCP, CCID 2, and CCID 3 drafts all became RFCs in March this year

* RFC 1063 was obsoleted by RFC 1191

* draft-ietf-tcpimpl-pmtud-0x.txt was published as an Informational
  RFC, RFC 2923 on 2000-09-22.

All references verified.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 2efb505..2fbb84b 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -23,7 +23,7 @@
  */
 
 /*
- * This implementation should follow: draft-ietf-dccp-ccid2-10.txt
+ * This implementation should follow RFC 4341
  *
  * BUGS:
  * - sequence number wrapping