sctp: fix to send FORWARD-TSN chunk only if peer has such capable

RFC3758 Section 3.3.1.  Sending Forward-TSN-Supported param in INIT

   Note that if the endpoint chooses NOT to include the parameter, then
   at no time during the life of the association can it send or process
   a FORWARD TSN.

If peer does not support PR-SCTP capable, don't send FORWARD-TSN chunk
to peer.
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: NVlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/outqueue.c

@@ -1758,6 +1758,9 @@ static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 ctsn)
 	struct sctp_chunk *chunk;
 	struct list_head *lchunk, *temp;
 
+	if (!asoc->peer.prsctp_capable)
+		return;
+
 	/* PR-SCTP C1) Let SackCumAck be the Cumulative TSN ACK carried in the
 	 * received SACK.
 	 *