MINOR: stream: use conn_full_close() instead of conn_force_close()

There's no point in using conn_force_close() in outgoing connect()
since XPRT_TRACKED is not set so both functions are equivalent.
diff --git a/src/stream.c b/src/stream.c
index 880327b..4ec6283 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -571,7 +571,7 @@
 		si->exp   = TICK_ETERNITY;
 		si->state = SI_ST_CER;
 
-		conn_force_close(srv_conn);
+		conn_full_close(srv_conn);
 
 		if (si->err_type)
 			return 0;