Refactor wireguard & add tun support

transport/wireguard/device.go

@@ -0,0 +1,14 @@
+package wireguard
+
+import (
+	N "github.com/sagernet/sing/common/network"
+
+	"golang.zx2c4.com/wireguard/tun"
+)
+
+type Device interface {
+	tun.Device
+	N.Dialer
+	Start() error
+	// NewEndpoint() (stack.LinkEndpoint, error)
+}