MINOR: session: make the number of stick counter entries more configurable

In preparation of more flexibility in the stick counters, make their
number configurable. It still defaults to 3 which is the minimum
accepted value. Changing the value alone is not sufficient to get
more counters, some bitfields still need to be updated and the TCP
actions need to be updated as well, but this update tries to be
easier, which is nice for experimentation purposes.
diff --git a/src/session.c b/src/session.c
index 9be5faa..ec78be1 100644
--- a/src/session.c
+++ b/src/session.c
@@ -420,7 +420,7 @@
 	/* Let's count a session now */
 	proxy_inc_fe_sess_ctr(l, p);
 
-	for (i = 0; i < sizeof(s->stkctr) / sizeof(s->stkctr[0]); i++) {
+	for (i = 0; i < MAX_SESS_STKCTR; i++) {
 		void *ptr;
 
 		if (!s->stkctr[i].entry)
@@ -707,7 +707,7 @@
 			if (s->listener->counters)
 				s->listener->counters->bytes_in += bytes;
 
-			for (i = 0; i < sizeof(s->stkctr) / sizeof(s->stkctr[0]); i++) {
+			for (i = 0; i < MAX_SESS_STKCTR; i++) {
 				if (!s->stkctr[i].entry)
 					continue;
 
@@ -741,7 +741,7 @@
 			if (s->listener->counters)
 				s->listener->counters->bytes_out += bytes;
 
-			for (i = 0; i < sizeof(s->stkctr) / sizeof(s->stkctr[0]); i++) {
+			for (i = 0; i < MAX_SESS_STKCTR; i++) {
 				if (!s->stkctr[i].entry)
 					continue;