Connectivity metrics: change how interface names are logged

This patch deprecates the ifname field for specific metrics events of
types DhcpClientEvent, DhcpErrorEvent, IpReachabilityEvent and
IpManagerEvent.

Instead ifnames are logged in ConnectivityMetricsEvent, allowing for
link layer inference.

Test: updated unit tests, $ runtest frameworks-net passes
Bug: 34901696
Change-Id: I8bfabcb115bbd5289471d653c153a40bb48f28cd