webrtcbin: rtpstorage takes a 64-bit integer for "size-time" property

https://bugzilla.gnome.org/show_bug.cgi?id=796429
diff --git a/ext/webrtc/gstwebrtcbin.c b/ext/webrtc/gstwebrtcbin.c
index c553a93..a28b936 100644
--- a/ext/webrtc/gstwebrtcbin.c
+++ b/ext/webrtc/gstwebrtcbin.c
@@ -3666,7 +3666,7 @@
     guint session_id, GstWebRTCBin * webrtc)
 {
   /* TODO: when exposing latency, set size-time based on that */
-  g_object_set (storage, "size-time", 250 * GST_MSECOND, NULL);
+  g_object_set (storage, "size-time", (guint64) 250 * GST_MSECOND, NULL);
 }
 
 static GstElement *