deepstream多路rtsp流，避免相互影响

1.拉多路rtsp流，一路视频断了，没一会整个程序就崩了。
解决，添加pad-removed属性：

static void
cb_newpad4 (GstElement * decodebin, GstPad * pad, gpointer data)
{
  NvDsSrcBin *bin = (NvDsSrcBin *) data;
  GstPad *sinkpad = gst_element_get_static_pad (bin->depay, "sink");
  if (gst_pad_unlink (pad, sinkpad) != GST_PAD_LINK_OK) {
    NVGSTDS_ERR_MSG_V ("Failed to link depay loader to rtsp src");
  }
  gst_object_unref (sinkpad);
}
  g_signal_connect (G_OBJECT (bin->src_elem), "pad-added",
      G_CALLBACK (cb_newpad3), bin);

  g_signal_connect (G_OBJECT (bin->src_elem), "pad-removed",
      G_CALLBACK (cb_newpad4), bin);