sctp: disable max_burst when the max_burst is 0

As Michael pointed out that when max_burst is 0, it just disable
max_burst. It declared in rfc6458#section-8.1.24. so add the check
in sctp_transport_burst_limited, when it 0, just do nothing.
Reviewed-by: Daniel Borkmann <dborkman@redhat.com>
Suggested-by: Vlad Yasevich <vyasevich@gmail.com>
Suggested-by: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/transport.c

@@ -573,7 +573,7 @@ void sctp_transport_burst_limited(struct sctp_transport *t)
 	u32 old_cwnd = t->cwnd;
 	u32 max_burst_bytes;
 
-	if (t->burst_limited)
+	if (t->burst_limited || asoc->max_burst == 0)
 		return;
 
 	max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);