Feature request: hostname.default

[Lars Engblom]

When needing to move a disk over from one computer to another, you quite 
often end up with hostname.X having the wrong name. Often it can be 
difficult to know what the interface will be called before booting up 
openbsd. As many servers are just accessable with ssh (and not through 
keyboard and screen) this is causing some problem at migrations.

Please consider to add support for a hostname.default. If no hostname.X 
is matching the interface, this file would be used as last resource 
before giving up configuring the interface.