8241336: Some java.net tests failed with NoRouteToHostException on MacOS with special network configuration

[Daniel Fuchs]

Hi,

Please find below a fix for:
8241336: Some java.net tests failed with NoRouteToHostException on
          MacOS with special network configuration
https://bugs.openjdk.java.net/browse/JDK-8241336

webrev:
http://cr.openjdk.java.net/~dfuchs/webrev_8241336/webrev.01/index.html

The crux of the issue is that on some macOS hardware/OS versions
we get network interfaces that look like regular ethernet interfaces
though they are not.
Picking them up while testing make some tests fail.

Most of these tests were already relying on the NetworkConfiguration
test library class - which has now been updated to skip these
problematic interfaces. I have heuristically observed that these
interfaces seemed to only have one link-local IPv6 address, while the
other regular interfaces had at least one IPv4, or one non link-local
IPv6. That seems to be the only observable difference.

The fix also contains some code for AdaptorMulticasting.java aim at
better diagnosing (and possibly fixing?) JDK-8238516 [1] - I might close
JDK-8238516 as a duplicate of JDK-8241336 if the issue doesn't
reproduce.

best regards,

-- daniel
[1] https://bugs.openjdk.java.net/browse/JDK-8238516