Fix flaky unit tests related to the flag: ignore organic nud failure.

The unit tests intended to check there should not be any notifyLost
callback to be triggered when the experiment flag is enabled, but the
flag value is initialized at the IpReachabilityMonitor constructor, that
requires the flag value to be set before running any test case. But the
test code enables the flag just before running the assert function, in
fact the flag value in the test is always false, but somehow the
mockito.never did catch the callback sometimes. Wait the HandleThread
become idle after replying with a organic NUD failure event and then
call never() to check, that ensures the notifyLost callback should never
be called.

This CL also updates the log message for critical organic NUD failure
events, which are to be ignored.

Bug: 315076572
Test: atest NetworkStackTests --rerun-until-failure
Change-Id: I88f5c40cb298c0c021de1baf15b256b3ece9ad2f
2 files changed