rtph263ppay: Don't pass upstream filter caps to downstream

Downstream usually can't accept video/x-h263 but only application/x-rtp,
so we would always get an empty intersection here.

https://bugzilla.gnome.org/show_bug.cgi?id=702632

gst/rtp/gstrtph263ppay.c

@@ -243,7 +243,7 @@ gst_rtp_h263p_pay_sink_getcaps (GstRTPBasePayload * payload, GstPad * pad,
   rtph263ppay = GST_RTP_H263P_PAY (payload);
 
   peercaps =
-      gst_pad_peer_query_caps (GST_RTP_BASE_PAYLOAD_SRCPAD (payload), filter);
+      gst_pad_peer_query_caps (GST_RTP_BASE_PAYLOAD_SRCPAD (payload), NULL);
 
   /* if we're just outputting to udpsink or fakesink or so, we should also
    * accept any input compatible with our sink template caps */