MEDIUM: servers: Store the connection in the SI until we have a mux.

When we create a connection, if we have to defer the conn_stream and the
mux creation until we can decide it (ie until the SSL handshake is done, and
the ALPN is decided), store the connection in the stream_interface, so that
we're sure we can destroy it if needed.
diff --git a/src/backend.c b/src/backend.c
index 3ab450b..cdc63c6 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1279,9 +1279,10 @@
 			/* Store the connection into the stream interface,
 			 * while we still don't have a mux, so that if the
 			 * stream is destroyed before the connection is
-			 * established, and a mux is set, we don't attempt
-			 * to access the stream
+			 * established, we have a chance to destroy it even
+			 * if it is no longer referenced in the session.
 			 */
+			s->si[1].end = &srv_conn->obj_type;
 			conn_set_xprt_done_cb(srv_conn, conn_complete_server);
 		}