Connectivity metrics: collect NFLOG wakeup events

This patch stores NFLOG packet wakeup events sent by Netd to the system
server into a ring buffer inside NetdEventListenerService. The content
of this buffer is accessible by $ dumpsys connmetrics or $ dumpsys
connmetrics list, and is added to bug reports.

The wakeup event buffer stores currently uid and timestamps.

Bug: 34901696
Bug: 62179647
Test: runtest frameworks-net, new unit tests
Change-Id: Ie8db6f8572b1a929a20398d8dc03e189bc488382