wm0 not connecting

["Ian D. Leroux" <idleroux%fastmail.fm@localhost>]

This is probably a case of PEBKAC, but I'm not sure how to debug it...

I have a laptop (Thinkpad X201) running amd64 current from about
mid-March.  Wireless networking with iwn0 works.  The (custom) kernel
config includes a device configuration line for wm0, and wm0 is listed
both in dmesg and in the output of ifconfig.  However, connecting a
cable to the laptop's Ethernet port does not give me a network
connection.  The blinkenlights on the adapter blink merrily away, but
ifconfig reports <... SIMPLEX ...>
...
media: Ethenet none (none)
...
and dhcpcd falls back to a self-assigned link-local address in 169.x.x.x
(that was transcribed from memory; I'll try to get a complete
transcript).

The hardware is functioning, since I can connect without problems
through the same Ethernet port when running another OS (the laptop
dual-boots to Windows 7). I don't think it's specific to the network's
configuration, since I've seen the same problem on two different,
independently administered networks.

Unfortunately, I've been mostly using the wireless card for the last
couple of years, so the last time I can be sure that wm0 worked was in
2011.

Does any of this ring any bells?  Are there any obvious or non-obvious
configuration switches in the kernel config or in /etc that would
cripple wm0 in this way?  Are any of the recent changes to if_wm.c
pertinent?

Thanks for any assistance,

--
IDL