Start the overlay package with the old Inside interface (#576)

overlay/device.go

@@ -0,0 +1,15 @@
+package overlay
+
+import (
+	"io"
+	"net"
+)
+
+type Device interface {
+	io.ReadWriteCloser
+	Activate() error
+	CidrNet() *net.IPNet
+	DeviceName() string
+	WriteRaw([]byte) error
+	NewMultiQueueReader() (io.ReadWriteCloser, error)
+}