vDPA/ifcvf: get_config_size should return dev specific config size

get_config_size() should return the size based on the decected
device type.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210419063326.3748-4-lingshan.zhu@intel.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>