MINOR: applet: add a new "owner" pointer in the appctx

This pointer indicates what stream-interface the appctx belongs to, just
like we have for the connections.

include/proto/stream_interface.h

@@ -234,6 +234,7 @@ static inline void si_attach_appctx(struct stream_interface *si, struct appctx *
 {
 	si->ops = &si_embedded_ops;
 	si->end = &appctx->obj_type;
+	appctx->owner = si;
 }
 
 /* returns a pointer to the appctx being run in the SI or NULL if none */

include/types/stream_interface.h

@@ -129,6 +129,7 @@ struct appctx {
 	unsigned int st1;          /* prompt for stats, session error for peers */
 	unsigned int st2;          /* output state for stats, unused by peers  */
 	struct si_applet *applet;  /* applet this context refers to */
+	void *owner;               /* pointer to upper layer's entity (eg: stream interface) */
 
 	union {
 		struct {