Better ConnectivityMetricsEvent printing

This patch adds more information printing for IpConnectivity event
classes in android.net.metrics.

example:

ConnectivityMetricsEvent(14:36:35.799, 0, 1026): DhcpClientEvent(wlan0, DhcpRequestingState)
ConnectivityMetricsEvent(14:36:35.805, 0, 1026): DhcpClientEvent(wlan0, DhcpHaveAddressState)
ConnectivityMetricsEvent(14:36:35.809, 0, 4096): IpManagerEvent(wlan0, PROVISIONING_OK, 155ms)
ConnectivityMetricsEvent(14:36:35.810, 0, 1026): DhcpClientEvent(wlan0, DhcpBoundState)
ConnectivityMetricsEvent(14:36:35.871, 0, 2048): NetworkEvent(101, NETWORK_CONNECTED, 0ms)
ConnectivityMetricsEvent(14:36:35.874, 0, 2051): ValidationProbeEvent(101, PROBE_HTTP:599, 3ms)
ConnectivityMetricsEvent(14:36:35.874, 0, 2048): NetworkEvent(101, NETWORK_VALIDATION_FAILED, 0ms)
ConnectivityMetricsEvent(14:36:35.928, 0, 3072): DefaultNetworkEvent(0 -> 101, [WIFI], IPv4: false, IPv6: false)
ConnectivityMetricsEvent(14:36:37.008, 0, 2051): ValidationProbeEvent(101, PROBE_HTTP:204, 134ms)
ConnectivityMetricsEvent(14:36:37.008, 0, 2050): NetworkEvent(101, NETWORK_VALIDATED, 1137ms)

Also fixes a couple of event logging issues:
  - do no record spurious receive DhcpErrorEvent when a network goes down.
  - add an eventType field to IpManagerEvent instead of using the
    loggger component tag.

Bug: 28204408
Change-Id: Ia6f4ccfd7a0c63a5ccec18825f226c0b5781217b