dccp ccid-2: use feature-negotiation to report Ack Ratio changes

This uses the new feature-negotiation framework to signal Ack Ratio changes,
as required by RFC 4341, sec. 6.1.2.

That raises some problems with CCID-2, which at the moment can not cope
gracefully with Ack Ratios > 1. Since these issues are not directly related
to feature negotiation, they are marked by a FIXME.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Samuel Jero <sj323707@ohio.edu>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.uk>
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 0462040..b51cc92 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -494,8 +494,16 @@
 			if (hc->tx_rpdupack >= NUMDUPACK) {
 				hc->tx_rpdupack = -1; /* XXX lame */
 				hc->tx_rpseq    = 0;
-
+#ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
+				/*
+				 * FIXME: Ack Congestion Control is broken; in
+				 * the current state instabilities occurred with
+				 * Ack Ratios greater than 1; causing hang-ups
+				 * and long RTO timeouts. This needs to be fixed
+				 * before opening up dynamic changes. -- gerrit
+				 */
 				ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
+#endif
 			}
 		}
 	}