RFR[8246164]: ‘SendDatagramToBadAddress.java and ChangingAddress.java should be changed to explicitly require the new DatagramSocket implementation’

[Patrick Concannon]

Hi,

Could someone please review my fix for JDK-8246164 — ‘SendDatagramToBadAddress.java and ChangingAddress.java should be changed to explicitly require the new DatagramSocket implementation’.

The issues addressed by the tests `java/net/DatagramSocket/SendDatagramToBadAddress.java` and `java/nio/channels/DatagramChannel/ChangingAddress.java` have been fixed by the new implementation of DatagramSocket. They are still known to fail on macOS with the old implementation, however. 

This fix updates these tests to explicitly run with `-Djdk.net.usePlainDatagramSocketImpl=false` to avoid false failures when running all tests with a global jtreg -Djdk.net.usePlainDatagramSocketImpl switch.

issue: https://bugs.openjdk.java.net/browse/JDK-8246164
webrev: cr.openjdk.java.net/~pconcannon/8246164/webrevs/webrev.00/

Kind regards,
Patrick