Configure Ethernet management interfaces using static IP "up"

The static IP passed from u-boot is not working in ONIE because
all interfaces are "down" after setting MAC addr.
Good find!

This does point out a little asymmetry in the way the config_ethmgmt_static() function works.

I think if we rework that slightly then we can handle this more cleanly.

Let me cook up a patch and send it took you.