MINOR: session: export the function 'smp_fetch_sc_stkctr'

This one is sometimes useful outside of this file.
diff --git a/include/proto/session.h b/include/proto/session.h
index c835bf0..2389a79 100644
--- a/include/proto/session.h
+++ b/include/proto/session.h
@@ -45,6 +45,7 @@
 void sess_change_server(struct session *sess, struct server *newsrv);
 struct task *process_session(struct task *t);
 void default_srv_error(struct session *s, struct stream_interface *si);
+struct stkctr *smp_fetch_sc_stkctr(struct session *l4, const struct arg *args, const char *kw);
 int parse_track_counters(char **args, int *arg,
 			 int section_type, struct proxy *curpx,
 			 struct track_ctr_prm *prm,
diff --git a/src/session.c b/src/session.c
index df85170..aeaa7e1 100644
--- a/src/session.c
+++ b/src/session.c
@@ -2758,7 +2758,7 @@
  * to be able to convery multiple values per key (eg: have gpc0 from
  * multiple tables).
  */
-static struct stkctr *
+struct stkctr *
 smp_fetch_sc_stkctr(struct session *l4, const struct arg *args, const char *kw)
 {
 	static struct stkctr stkctr;