This adds a dummy network device so that we can use gro_cells for IPsec GRO. We now may have a secpath at a GRO merged skb, so we need to drop it. This is the only change to the generic networking code.
The packet still travels two times through the stack, but might be aggregated in the second round. We can avoid the second round with implementing GRO callbacks for the IPsec protocols. This will be a separate patchset as this needs some more generic networking changes because of the asynchronous nature of IPsec.
