BUG/MEDIUM: sink: Properly get the stream-int in appctx callback functions

The appctx owner is not a stream-interface anymore. It is now a
conn-stream. However, sink code was not updated accordingly. It is now
fixed.

It is 2.6-specific, no backport is needed.
diff --git a/src/sink.c b/src/sink.c
index aa0ecfa..dd6f6b0 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -294,7 +294,7 @@
  */
 static void sink_forward_io_handler(struct appctx *appctx)
 {
-	struct stream_interface *si = appctx->owner;
+	struct stream_interface *si = cs_si(appctx->owner);
 	struct stream *s = si_strm(si);
 	struct sink *sink = strm_fe(s)->parent;
 	struct sink_forward_target *sft = appctx->ctx.sft.ptr;
@@ -433,7 +433,7 @@
  */
 static void sink_forward_oc_io_handler(struct appctx *appctx)
 {
-	struct stream_interface *si = appctx->owner;
+	struct stream_interface *si = cs_si(appctx->owner);
 	struct stream *s = si_strm(si);
 	struct sink *sink = strm_fe(s)->parent;
 	struct sink_forward_target *sft = appctx->ctx.sft.ptr;
@@ -580,7 +580,7 @@
 	if (!sft->appctx)
 		return;
 
-	si = sft->appctx->owner;
+	si = cs_si(sft->appctx->owner);
 	if (!si)
 		return;