Adjust query frequency based on remaining TTL

After numOfQueriesBeforeBackoff query, the mDNS discovery logic will
enter backoff mode. In backoff mode,  the query frequency will be
updated to max(20, 0.8 * shortest remaining TTL) seconds. It will help
to reduce mDNS query frequency in certain use cases.

Bug: 284480315
Test: atest CtsNetTest FrameworksNetTests
Change-Id: Iac8baaaf58cf9b3b8e67e1cd80402fdecde1d3d4