RFR : 8182672: Java 8u121 on Linux intermittently returns null for MAC address

[Seán Coffey]

JDK 10 fix required to correct a race issue in NetworkInterface. I don't 
believe the ifreq struct needs to be static in any case. New auto unit 
testcase also. I propose to skip this fix for JDK 9 and fix in an update 
release for that family. I also plan to port this to jdk8u-dev.

https://bugs.openjdk.java.net/browse/JDK-8182672
webrev : http://cr.openjdk.java.net/~coffeys/webrev.8182672.jdk10/webrev/
regards,
Sean.