MEDIUM: connection: make use of the owner instead of container_of

This way the connection can become independant on the stream interface.
diff --git a/src/session.c b/src/session.c
index be25ccf..91684ad 100644
--- a/src/session.c
+++ b/src/session.c
@@ -260,7 +260,7 @@
  */
 int conn_session_complete(struct connection *conn, int flag)
 {
-	struct session *s = container_of(conn, struct session, si[0].conn);
+	struct session *s = container_of(conn->owner, struct session, si[0]);
 
 	if (!(conn->flags & CO_FL_ERROR) && (session_complete(s) > 0)) {
 		conn->flags &= ~flag;