Comment 2 for bug 1750119

> It does display a message for a wired interface that is
> not connected, but does not say anything when an interface
> is connected.

As of 2018.03.19 daily (Ubuntu 18.04.0 Bionic "Live-Server") at least, this page now lists a link-speed of negative-one Megabit-per-second for link-down^:

nic-name > Not connected
   IPv4 is not configured
   IPv6 is not configured
   nn:nn:nn:nn:nn:nn Vendor-Name Device-Name (reported link-speed)

… with the last line rendered as ANSI dim-text.

For example, vmxnet3 will be:

   00:50:56:nn:nn:nn VMware VMXNET3 Ethernet (-1M)

… for a link-down condition, and …

   00:50:56:nn:nn:nn VMware VMXNET3 Ethernet (10G)

… for a link-up condition.

(^) Still suffers from jumpiness and reflow issues (bug 1750114), and link-speed isn't updated if you transition one of the NICs from link-down to link-up (or the reverse) after reaching that page for the first time.