Run detach hook and similar before cleaning up any other resource when

Run detach hook and similar before cleaning up any other resource when
an interface is destroyed/removed.  This way we can ensure pseudo-driver
changes done after attaching an interface are undone before detaching it.

Note: it is safe to call if_deactivate() multiple times as the interface
should not have any attached pseudo-interface after the first call.

ok deraadt@, dlg@