rtpsession: fix up GHashTable-behavior dependent tests
rtpsession: fix up GHashTable-behavior dependent tests

GHashTable iteration order changed in recent GLib,
and tests were relying on that.

https://mail.gnome.org/archives/desktop-devel-list/2018-October/msg00016.html

pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good