[DCCP]: Add FIXME for send_delayed_ack

This adds a FIXME to signal that the function dccp_send_delayed_ack is nowhere
used in the entire DCCP/CCID code.

Using a delayed Ack timer is suggested in 11.3 of RFC 4340, but it has also
rather subtle implications for the Ack-Ratio-accounting.

CCID2 does not use this (maybe it should).

I think leaving the function in is good, in case someone wants to implement
this.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 6e23d5b..d0c9ec6 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -477,6 +477,7 @@
 
 EXPORT_SYMBOL_GPL(dccp_send_ack);
 
+/* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
 void dccp_send_delayed_ack(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);