Summary of major changes in this CL:
1. update javadoc in AdvertisingRequest to start with one line
2. update ttl API document to ve clearer that values smaller than 1
second is discarded
3. Remove redundant constructors of MdnsServiceInfo
4. add tests for MdnsRecordRepository to verify that addService works
with non-null TTL
Other comments needs more consideration and relatively larger change, so
tracked in separated child issue of b/327619631
Bug: 327619631
Change-Id: I040b8451337d88d96da7120455c228cef204f768
c6622e02b7