Add comments to getters as requested in API review, and remove the expirationTime private field that was planned to be replaced with LinkAddress expiration. Test: atest TetheringTests Fixes: 150878126 Change-Id: Iecf65859cdeeaac2fa7b817b4f505c510424ac89 Merged-In: Iecf65859cdeeaac2fa7b817b4f505c510424ac89 (cherry picked from commit 594d0eae38c13e2bb03de0b3ae1f8781991c321e)