get_interfaces() keys entries by the physical device ("em0"), which is what
every other call in this driver speaks. Wake-on-LAN is the exception: it needs
the name OPNsense assigned ("lan", "opt1") and silently rejects anything else
with an empty {} at HTTP 200.
The overview export already carries it, so pass it through as "identifier".
Empty for interfaces OPNsense has not assigned.