Fix Automated API Review issues.

These API's argument/return value must be marked either @NonNull
or @Nullable.

Bug: 126701148
Bug: 126699090
Bug: 126701058
Bug: 126700772
Bug: 126699941
Bug: 126701299
Bug: 126700007
Bug: 126700900
Test: atest FrameworksNetTests
Change-Id: Id030a9f1116178b96aa3d4614b10969a537b2fc4