Expose NetworkScore to external caller

NetworkScore will be a part of mainline module, so the external
callers cannot call its hidden APIs. Expose needed APIs to
the external callers.

CTS-Coverage-Bug: 182963397
Bug: 182963397
Test: m
Change-Id: Iddf8c71a5f51a40bc6ff78626b3e8ee530d1b7eb
Merged-In: Iddf8c71a5f51a40bc6ff78626b3e8ee530d1b7eb
  (cherry-picked from ag/13947595)