MEDIUM: conn_stream: Add a pointer to the app object into the conn-stream

In the same way the conn-stream has a pointer to the stream endpoint , this
patch adds a pointer to the application entity in the conn-stream
structure. For now, it is a stream or a health-check. It is mandatory to
merge the stream-interface with the conn-stream.
diff --git a/src/check.c b/src/check.c
index 97d340a..cbdf620 100644
--- a/src/check.c
+++ b/src/check.c
@@ -1019,7 +1019,7 @@
 static int wake_srv_chk(struct conn_stream *cs)
 {
 	struct connection *conn;
-	struct check *check = cs->data;
+	struct check *check = cs_check(cs);
 	struct email_alertq *q = container_of(check, typeof(*q), check);
 	int ret = 0;