a vector of indices into the cfdata table to specify potential parents,
record the interface attributes that devices have and add a new "parent
spec" structure which lists the iattr, as well as optionally listing
specific parent device instances.
See:
http://mail-index.netbsd.org/tech-kern/2002/09/25/0014.html
...for a detailed description.
While here, const poison some things, as suggested by Matt Thomas.
