MINOR: stconn: Move data from kip to kop when data are sent to the consumer

When data are sent to the consumer, the known output payload length is
updated using the known input payload length value and this last one is then
reset. se_fwd_kip() function is used for this purpose.

src/stconn.c

@@ -1643,6 +1643,8 @@ int sc_conn_send(struct stconn *sc)
 	if (!conn->mux)
 		return 0;
 
+	se_fwd_kip(sc->sedesc);
+
 	if (sc_ep_have_ff_data(sc)) {
 		unsigned int send_flag = 0;