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/output.c b/net/sctp/output.c
index 2a5c189..84f66d5 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -552,7 +552,8 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
 				 * for a given destination transport address.
 				 */
 
-				if (!chunk->resent && !tp->rto_pending) {
+				if (!sctp_chunk_retransmitted(chunk) &&
+				    !tp->rto_pending) {
 					chunk->rtt_in_progress = 1;
 					tp->rto_pending = 1;
 				}