Change throw to Log.wtf

Log.wtf should avoid crashes, while making sure that one can still
notice if there is a problem.

In particular, it may be possible that calling ensureIpServerStopped
and ensureIpServerStarted could start forwarding before the previous
IpServer has stopped it.

Bug: 314260975
Change-Id: I047a673d2fe6f218192d3144fa0bd60ce8739a15
Test: TH