Make notification icons and autocancel overlayable

Allow overlays to change the connectivity notification icons, and
whether the notifications are auto-cancelled.

This does not change default behavior, but is necessary to allow vendors
to adapt the notifications to their standards.

Bug: 173171709
Bug: 172048052
Test: atest NetworkNotificationManagerTest
      Added test overlay, verified icon replaced
Original-Change: https://android-review.googlesource.com/1753822
Merged-In: Ibbb765a5e828b8b870cbfb81e89df2dbd2828be7
Change-Id: Ibbb765a5e828b8b870cbfb81e89df2dbd2828be7
4 files changed