vaapipostproc: set discont flag at vpp deinterlacing
vaapipostproc: set discont flag at vpp deinterlacing

When deinterlacing with VPP the discont flag was not forwarded to
the new created buffer. This patch sets the discont flag if input
buffer has it.

ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi