TT#14008 fix seq_file usage

If the seq_file buffer overflows, the printing of the last item is
re-tried following a stop/start event on the seq_file. Therefore we
cannot unconditionally increase the offset whenever our `next` method is
called.

closes #1244

Change-Id: I7026deeeb03423cc2da57b1e069019638cf734cf
(cherry picked from commit 9d4b870b0f)

kernel-module/xt_RTPENGINE.c

@@ -1283,7 +1283,6 @@ next_rda:
 
 	*addr_bucket = ab;
 	*port = (hi << 8) | lo;
-	(*port)++;
 
 	return g;
 }
@@ -1347,6 +1346,7 @@ static ssize_t proc_blist_read(struct file *f, char __user *b, size_t l, loff_t
 	addr_bucket = ((int) *o) >> 17;
 	port = ((int) *o) & 0x1ffff;
 	g = find_next_target(t, &addr_bucket, &port);
+	port++;
 	*o = (addr_bucket << 17) | port;
 	err = 0;
 	if (!g)
@@ -1429,7 +1429,7 @@ static void *proc_list_start(struct seq_file *f, loff_t *o) {
 static void proc_list_stop(struct seq_file *f, void *v) {
 }
 
-static void *proc_list_next(struct seq_file *f, void *v, loff_t *o) {	/* v is invalid */
+static void *proc_list_next(struct seq_file *f, void *v, loff_t *o) {
 	u_int32_t id = (u_int32_t) (unsigned long) f->private;
 	struct rtpengine_table *t;
 	struct rtpengine_target *g;
@@ -1442,6 +1442,9 @@ static void *proc_list_next(struct seq_file *f, void *v, loff_t *o) {	/* v is in
 	if (!t)
 		return NULL;
 
+	if (v) // this is a `next` call
+		port++;
+
 	g = find_next_target(t, &addr_bucket, &port);
 
 	*o = (addr_bucket << 17) | port;