DO NOT MERGE IP Connectivity metrics: add connect() statistics

This patch adds a ConnectStats class to aggregate connect() statistics
gathered in NetdEventListenerService. ConnectStats is uploaded once a
day by IpConnectivityMetrics.

Test: $ runtest frameworks-net + new unit test
Bug: 32198976

(cherry picked from commit 4f71a15973f7048076ed10f63d708f020e1a21e0)

Change-Id: I1450c126b90b628d9f1c73ddf054b4742f5e84c5