NetworkStackNotifier is not nullable anymore am: c6b23e6236

Original change: https://android-review.googlesource.com/c/platform/packages/modules/NetworkStack/+/3291187

Change-Id: I58feb415202a8236b31b8c9c435e81211e251a16
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>