The relation between uhci(4), ohci(4) and their root hub device is

The relation between uhci(4), ohci(4) and their root hub device is
delicate.  HC drivers do not always accept to be left alone.

I don't know if it is a love crisis, but apparently receiving a root
hub status change interrupt before having an uhub(4) attached breaks
resume.

So make sure the root hub is re-attached before interrupt get enabled.
It is safe to do it during DVACT_RESUME since attaching root hubs do
not require any USB transfer.

Based on a diff from yasuoka@, fix a regression introduced in last
commit an reported by Abel Abraham Camarillo Ojeda on tech@ and Nils
R on bugs@.