Put modules back on children for wall switches (#881)

Puts modules back on the children for `WallSwitches` (i.e. ks240) and
makes them accessible from the `modules` property on the parent.

kasa/iot/iotstrip.py

@@ -253,7 +253,7 @@ class IotStripPlug(IotPlug):
         self._last_update = parent._last_update
         self._set_sys_info(parent.sys_info)
         self._device_type = DeviceType.StripSocket
-        self.modules = {}
+        self._modules = {}
         self.protocol = parent.protocol  # Must use the same connection as the parent
         self.add_module("time", Time(self, "time"))