wgengine: remove Config.TUN argument.

cmd/tailscaled/tailscaled.go

@@ -343,7 +343,6 @@ func tryEngine(logf logger.Logf, linkMon *monitor.Mon, name string) (e wgengine.
 			tstun.Diagnose(logf, name)
 			return nil, false, err
 		}
-		conf.TUN = dev
 	}
 	e, err = wgengine.NewUserspaceEngine(logf, dev, conf)
 	if err != nil {

wgengine/userspace.go

@@ -133,9 +133,6 @@ func (e *userspaceEngine) GetInternals() (*tstun.Wrapper, *magicsock.Conn) {
 
 // Config is the engine configuration.
 type Config struct {
-	// TUN is the TUN device used by the engine.
-	TUN tun.Device
-
 	// Router is the interface to OS networking APIs used to interface
 	// the OS with the Engine.
 	Router router.Router