Fix GATT listen mode updating

Update gatt's listen-mode flag whenever connect_cb() is called again.
diff --git a/attrib/client.c b/attrib/client.c
index 44638d3..ec5fcf2 100644
--- a/attrib/client.c
+++ b/attrib/client.c
@@ -356,6 +356,7 @@
 
 	if (gatt->attrib != NULL) {
 		gatt->attrib = g_attrib_ref(gatt->attrib);
+		gatt->listen = listen;
 		return 0;
 	}