[SCTP] Don't search gap ack blocks past max_tsn_seen.

There is no need to keep walking the tsnmap past the 
max_tsn_seen, so don't.

net/sctp/tsnmap.c

 /* SCTP kernel reference Implementation
  * Copyright (c) 1999-2000 Cisco, Inc.
  * Copyright (c) 1999-2001 Motorola, Inc.
- * Copyright (c) 2001 International Business Machines, Corp.
+ * Copyright (c) 2001-2003 International Business Machines, Corp.
  * Copyright (c) 2001 Intel Corp.
  *
  * This file is part of the SCTP kernel reference Implementation
@@ -194,6 +194,10 @@ int sctp_tsnmap_next_gap_ack(const struct sctp_tsnmap *map,
 	/* We haven't found a gap yet.  */
 	started = ended = 0;
 
+	/* If there are no more gap acks possible, get out fast.  */
+	if (TSN_lte(map->max_tsn_seen, iter->start))
+		return 0;
+
 	/* Search the first mapping array.  */
 	if (iter->start - map->base_tsn < map->len) {