Disable cache flush bit in existing announcement

Per RFC6762#10.1, the cache flush bit should be false for
existing announcement. Otherwise, the record will be deleted
immediately when receiving this response.

Bug: 299054783
Test: atest FrameworksNetTestCases NsdManagerTest
Change-Id: I8bf1a5b1914b49720862836abb543b232185f5f5
2 files changed