To upload a GPX file to Garmin Connect, first log in to Garmin Connect.
Then click on the Upload button.
Select Manual Upload and Browse for the GPX file to upload.
From the "What's New" page on Garmin Connect it says:
GPX Support
Upload data from Garmin outdoor handhelds and other manufacturers that support the .gpx file format.
I think this means it only supports gpx files from a device. The gpx file you attached contains only waypoints. The gpx files that I've seen from devices contain trackpoints. Trackpoints are the points actually recorded by the gps device and contain the time/date information with each point. The waypoints don't contain any time/date information. The tcx files contain trackpoints as well.