Remove the code to automagically find a "carpdev".

Remove the code to automagically find a "carpdev".

The half-backed logic to find a parent interface before configuring an
address on a carp(4) interface is responsible for too many layers of
complexity resulting in various breakages everytime something change in
the stack.

So make carp(4) a bit less special.  It now requires a parent interface
like all the other pseudo-devices.

ok mikeb@, dlg@, florian@, henning@