Implemented getActiveScorerPackage() in the NetworkScoreService to
make it more efficient (no need to query PM).
Test: runtest frameworks-services -c com.android.server.NetworkScoreServiceTest
Bug: 33781558
Change-Id: Iee7610e4982b44aefa1ef8b6c208292b8f9adcf8
Merged-In: I2144351c2c09cad30f80399069364f3572e38445