Use InetAddress instead of String in network events.

This is a conservative change that converts strings to
InetAddress on the fly just before givint it to the client.

Also renamed getIpAddressesCount to getTotalResolvedAddressCount
to make it 1) harder to misuse it as getInetAddresses().length
2) more descriptive.

Bug: 37625453
Test: runtest --path frameworks/base/services/tests/servicestests/src/com/android/server/devicepolicy/NetworkEventTest.java
Test: cts-tradefed run cts -m CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.DeviceOwnerTest#testNetworkLoggingWithSingleUser
Change-Id: I2a31dddd6874f1a629895e4dff105cf41984a775