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