USB network devices or VirtualBox bridges are just
temporarily up and active in the system.
The Network Monitor Widget automatically adds such interfaces
when such devices get connected.
Unfortunately it does not remove them when disconnected.
This patch tries to implement also the removal and
works in current Debian testing/buster.
But it touches the common file Applet.qml, so it may have unwanted
side effects to other widgets in its current state.
BUG: 411106
FIXED-IN: 5.17.0