Use network list in UNDERLYING_NETWORKS_CHANGED

The bundle is no longer necessary, as this message is not sent across
processes: the network list can be sent directly in the message obj
pair.

Bug: 173574274
Test: atest FrameworksNetTests CtsNetTestCasesLatestSdk
Change-Id: Iae049a24212ff9df19b29aead20bf4a594f05f99