Add mock class to avoid Null Point Exception

Null point exception happend when DatagramDispatcherTest/ReceiverTest were called
ControllerMetricsStats class does not exist for unit test because it is created from SatelliteController

Bug: 278323102
Test: atest DatagramDispatcherTest DatagramReceiverTest
Change-Id: I91fb0fc786882fbd827d0b16f0e78bba8e3fae5c