Apps targeting sdk < U are considered to use a legacy native daemon as NsdManager backend, but other apps use a platform-integration mDNS implementation as backend. So add a CompatChange flag to enable platform backend for non-legacy apps. Bug: 270306772 Test: atest FrameworksNetTests CtsNetTestCases Change-Id: I7ba58f8a5186fb49ad5f8aeacc8b8234bef1eabe