Add AWSVPC setup routines to the attach script

When running in the AWSVPC mode, we need to do the following:

- Keep the HW TX offloading on.
- Check that the allocated address belongs to the default subnet,
  because only one subnet is allowed and it should be the default one.

If it is not possible to determine whether AWSVPC is on, we ignore
all the steps, because the attachment routines have to work
regardless whether the router is running and the AWSVPC detection
is done by querying the /ipinfo/tracker endpoint served by
the router.

plugin/net/cni.go

@@ -92,7 +92,7 @@ func (c *CNIPlugin) CmdAdd(args *skel.CmdArgs) error {
 		id = fmt.Sprintf("%x", data)
 	}
 
-	if err := weavenet.AttachContainer(ns, id, args.IfName, conf.BrName, conf.MTU, false, []*net.IPNet{&result.IP4.IP}); err != nil {
+	if err := weavenet.AttachContainer(ns, id, args.IfName, conf.BrName, conf.MTU, false, []*net.IPNet{&result.IP4.IP}, false); err != nil {
 		return err
 	}
 	if err := weavenet.WithNetNSLink(ns, args.IfName, func(link netlink.Link) error {

plugin/net/driver.go

@@ -134,8 +134,9 @@ func (driver *driver) JoinEndpoint(j *api.JoinRequest) (*api.JoinResponse, error
 	if err != nil {
 		return nil, driver.error("JoinEndpoint", "unable to find network info: %s", err)
 	}
+
 	name, peerName := vethPair(j.EndpointID)
-	if _, err := weavenet.CreateAndAttachVeth(name, peerName, weavenet.WeaveBridgeName, 0, nil); err != nil {
+	if _, err := weavenet.CreateAndAttachVeth(name, peerName, weavenet.WeaveBridgeName, 0, false, nil); err != nil {
 		return nil, driver.error("JoinEndpoint", "%s", err)
 	}