Hi Jan:

The attached addresses the spinning with the usb net device. Now I can
enable the device and ethtool shows a link:

# ifconfig usb0 up
# ethtool usb0
Settings for usb0:
	Current message level: 0x00000007 (7)
	Link detected: yes

Though dhclient still can't get an address. After a bit of
instrumentation it appears that packets are lost in the receive the path
somewhere:

usb0      Link encap:Ethernet  HWaddr 42:5F:CA:51:54:77
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:5513 (5.3 KiB)

I looked at an x3650M2 with an IMM. It has a usb-based ethernet device.
I compared the output of lsusb -v from the IMM with the qemu usb net
device and nothing jumps out -- other than the fact that the IMM's
network device shows up on a uhci bus.

David