refactor: simplify fastdp initialisation

prog/weaver/main.go

@@ -162,7 +162,7 @@ func main() {
 	}
 	config.ProtocolMinVersion = byte(protocolMinVersion)
 
-	var fastDPOverlay weave.NetworkOverlay
+	overlays := weave.NewOverlaySwitch()
 	if datapathName != "" {
 		// A datapath name implies that "Bridge" and "Overlay"
 		// packet handling use fast datapath, although other
@@ -176,8 +176,11 @@ func main() {
 
 		checkFatal(err)
 		networkConfig.Bridge = fastdp.Bridge()
-		fastDPOverlay = fastdp.Overlay()
+		overlays.Add("fastdp", fastdp.Overlay())
 	}
+	sleeve := weave.NewSleeveOverlay(config.Port)
+	overlays.Add("sleeve", sleeve)
+	overlays.SetCompatOverlay(sleeve)
 
 	if ifaceName != "" {
 		// -iface can coexist with -datapath, because
@@ -205,14 +208,6 @@ func main() {
 		Log.Println("Communication between peers via untrusted networks is encrypted.")
 	}
 
-	overlays := weave.NewOverlaySwitch()
-	if fastDPOverlay != nil {
-		overlays.Add("fastdp", fastDPOverlay)
-	}
-	sleeve := weave.NewSleeveOverlay(config.Port)
-	overlays.Add("sleeve", sleeve)
-	overlays.SetCompatOverlay(sleeve)
-
 	if routerName == "" {
 		if iface == nil {
 			Log.Fatal("Either an interface must be specified with --iface or a name with -name")