sctp: reuse sent_count to avoid retransmitted chunks for RTT measurements

Now sctp uses chunk->resent to record if a chunk is retransmitted, for
RTT measurements with retransmitted DATA chunks. chunk->sent_count was
introduced to record how many times one chunk has been sent for prsctp
RTX policy before. We actually can know if one chunk is retransmitted
by checking chunk->sent_count is greater than 1.

This patch is to remove resent from sctp_chunk and reuse sent_count
to avoid retransmitted chunks for RTT measurements.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
index 5825853..e540826 100644
--- a/net/sctp/outqueue.c
+++ b/net/sctp/outqueue.c
@@ -507,8 +507,6 @@ void sctp_retransmit_mark(struct sctp_outq *q,
 				transport->rto_pending = 0;
 			}
 
-			chunk->resent = 1;
-
 			/* Move the chunk to the retransmit queue. The chunks
 			 * on the retransmit queue are always kept in order.
 			 */
@@ -1439,7 +1437,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
 				 * instance).
 				 */
 				if (!tchunk->tsn_gap_acked &&
-				    !tchunk->resent &&
+				    !sctp_chunk_retransmitted(tchunk) &&
 				    tchunk->rtt_in_progress) {
 					tchunk->rtt_in_progress = 0;
 					rtt = jiffies - tchunk->sent_at;