Update the usage data when upstream is changed

Need to refresh the usage data. If the network switches back to
Wi-Fi after using cellular data (Wi-Fi -> Cellular -> Wi-Fi), the
old baseline might be inaccurate, leading to incorrect delta
calculations.

Also address some leftover comments.

Fix: 369306449
Fix: 370652336
Test: atest TetheringTests
Change-Id: I1c14aac533cee1d989b7ab354111f071da018058
2 files changed