[ifmgmt] Move link-up status messages from autoboot() to iflinkwait()

[ifmgmt] Move link-up status messages from autoboot() to iflinkwait()

With the addition of link status codes, we can now display a detailed
error indication if iflinkwait() fails.

Putting the error output in iflinkwait avoids code duplication, and
gains symmetry with the other interface management routines; ifopen()
already prints an error directly if it cannot open its interface.

Modified-by: Michael Brown <mcb30@etherboot.org>
Signed-off-by: Michael Brown <mcb30@etherboot.org>