[client] Refactor/iface pkg (#2646)

Refactor the flat code structure

client/iface/device/adapter.go

@@ -0,0 +1,8 @@
+package device
+
+// TunAdapter is an interface for create tun device from external service
+type TunAdapter interface {
+	ConfigureInterface(address string, mtu int, dns string, searchDomains string, routes string) (int, error)
+	UpdateAddr(address string) error
+	ProtectSocket(fd int32) bool
+}