[ipv6]: 8224014: Don't run test/jdk/java/net/NetworkInterface/IPv4Only.java in IPv6 only environment

[Arthur Eubanks]

webrev: http://cr.openjdk.java.net/~aeubanks/8224014/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8224014

In https://bugs.openjdk.java.net/browse/JDK-8220673, I missed
skipping test/jdk/java/net/NetworkInterface/IPv4Only.java when running in
an IPv6 only environment. It should have a call to
IPSupport.throwSkippedExceptionIfNonOperational().
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