Fix multipathPolicyTracker query-update loop

Query stats from NetworkStatsService will trigger a poll by default.
But since MultipathPolicyTracker listens NPMS events that triggered by
stats updated event, and will query stats
after the event. A polling -> updated -> query -> polling loop will be introduced
if polls on open. Hence, set flag to false to prevent a polling loop.

Test: 1. Boot up device with SIM card.
      2. atest FrameworksNetTests
Bug: 214638058
Change-Id: I60f2a4d08783575933602523dcca73d45a2caae5