Have the NetworkScoreService bind to the scorer.

If the current active scorer provides a service that can handle the
android.net.scoring.SCORE_NETWORKS action then the NetworkScoreService
will bind to that service to keep the scorer alive. If no service is
discovered then no attempt to bind will be made.

BUG: 27612145
Change-Id: I3f6ed0cbd83e658f1533c3e37b0cac2692c01761