Partial cherry pick from commit 1a6e667cb6
adding a new INetdEventCallback type.
Bug: 63908748
Test: built, flashed, $ runtest frameworks-net
Change-Id: I1b95cc4e5cbbfbdbd7429d61e2dcb67b90d278bb
Merged-In: I09595178bac0070a867bc5e0501a7bf2c840e398