vhost-vdpa works only with specific devices. At startup, it second
guesses what the command line option handling will do and error out if
it thinks a non-virtio device will attach to them.
This second guessing is not only ugly, it can lead to wrong error
messages ('-device floppy,netdev=foo' should complain about an unknown
property, not about the wrong kind of network device being attached) and
completely ignores hotplugging.
Drop the old checks and implement .check_peer_type() instead to fix
this. As a nice side effect, it also removes one more dependency on the
legacy QemuOpts infrastructure and even reduces the code size.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>