The current avahi implementation uses a one-shot browse that completes
in approximately one second. This is insufficient for thread devices
that need time to propagage SRP messages through the BR. The majority
of the dnssd timeout is unused. This implements a browse retry with
backoff and also implements the StopBrowse function.

Test: chip-tool pairing started before app, now works. StopBrowse
      is checked in the TestDnssd platform tests.