MEDIUM: applet: Set the conn-stream as appctx owner instead of the stream-int

Because appctx is now an endpoint of the conn-stream, there is no reason to
still have the stream-interface as appctx owner. Thus, the conn-stream is
now the appctx owner.
diff --git a/src/pool.c b/src/pool.c
index 0e33cd3..45c05fa 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -995,7 +995,7 @@
  */
 static int cli_io_handler_dump_pools(struct appctx *appctx)
 {
-	struct stream_interface *si = appctx->owner;
+	struct stream_interface *si = cs_si(appctx->owner);
 
 	dump_pools_to_trash();
 	if (ci_putchk(si_ic(si), &trash) == -1) {