When running qemu-system-m68k with the "-net" parameter (for example
simply "-net nic -net user"), there is currently a confusing warning
message saying:

 Warning: requested NIC (anonymous, model mcf_fec) was not created
 (not supported by this machine?)

This seems to happen because the MCF NIC has never been adapted to
the currently expected QEMU device behavior. Thus let's QOMify the
NIC now to get rid of the warning message.
Signed-off-by: NThomas Huth <huth@tuxfamily.org>
Signed-off-by: NJason Wang <jasowang@redhat.com>