[mdns] add elapsedRealTime() to Dependencies for MdnsRecordRepository

This CL adds elapsedRealTime() to Dependencies so that in the unit test
we can simulate the elapse of time.

Bug: 336268432
Test: atest FrameworksNetTests:android.net.connectivity.com.android.server.connectivity.mdns.MdnsRecordRepositoryTest
Change-Id: I64cf0ac1772f54edf187cf9ca6351a75b81fd859
2 files changed