sctp: shrink stream outq only when new outcnt < old outcnt

It's not necessary to go list_for_each for outq->out_chunk_list
when new outcnt >= old outcnt, as no chunk with higher sid than
new (outcnt - 1) exists in the outqueue.

While at it, also move the list_for_each code in a new function
sctp_stream_shrink_out(), which will be used in the next patch.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/stream.c

@@ -22,17 +22,11 @@
 #include <net/sctp/sm.h>
 #include <net/sctp/stream_sched.h>
 
-/* Migrates chunks from stream queues to new stream queues if needed,
- * but not across associations. Also, removes those chunks to streams
- * higher than the new max.
- */
-static void sctp_stream_outq_migrate(struct sctp_stream *stream,
-				     struct sctp_stream *new, __u16 outcnt)
+static void sctp_stream_shrink_out(struct sctp_stream *stream, __u16 outcnt)
 {
 	struct sctp_association *asoc;
 	struct sctp_chunk *ch, *temp;
 	struct sctp_outq *outq;
-	int i;
 
 	asoc = container_of(stream, struct sctp_association, stream);
 	outq = &asoc->outqueue;
@@ -56,6 +50,19 @@ static void sctp_stream_outq_migrate(struct sctp_stream *stream,
 
 		sctp_chunk_free(ch);
 	}
+}
+
+/* Migrates chunks from stream queues to new stream queues if needed,
+ * but not across associations. Also, removes those chunks to streams
+ * higher than the new max.
+ */
+static void sctp_stream_outq_migrate(struct sctp_stream *stream,
+				     struct sctp_stream *new, __u16 outcnt)
+{
+	int i;
+
+	if (stream->outcnt > outcnt)
+		sctp_stream_shrink_out(stream, outcnt);
 
 	if (new) {
 		/* Here we actually move the old ext stuff into the new