improve USB3 SSD support

Submitted by tim..@..il.com

Assigned to Xfce-Goodies Maintainers

Link to original bug (#11039)

Description

This is really a request: I run Xfce Linux from within an external USB3 solid state drive. I would like to monitor how fast and how often the SSD is working, but currently the plugin seems not to do this in the graph. The pop-up has momentary changes, so I know that it's sensing the drive, but there is no reflection of these occurances in the graph. Please improve this plugin so that it will record USB3 SSD activity.