ptp: fix build failure with #undef USE_MEASUREMENT_FILTERING
ptp: fix build failure with #undef USE_MEASUREMENT_FILTERING

"Label ‘out’ used but not defined", since it's also used by
the USE_MEDIAN_PRE_FILTERING branch.

https://bugzilla.gnome.org/show_bug.cgi?id=785631

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer