Move BaseNetdUnsolicitedEventListener to frameworks/libs/net and
create a new library - netd-client for using.
Also remove netd_aidl_interface-unstable-java since netd-client
links to the stable one.
Bug: 174837473
Test: Manual test and check the log.
Change-Id: Id65142b8c13a6cccbfe387d4ab757967497546e6