RFR (XS): 8169865: Downport minor fixes in java.net native code from JDK 9 to JDK 8

[Langer, Christoph]

Hi,

please review a downport of a few small fixes to JDK 8 which were done through bugs 8034174, 8034182 and 8048518 to JDK 9 already.

Bug: https://bugs.openjdk.java.net/browse/JDK-8169865
Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8169865.8udev/

The change in Inet6AddressImpl.c is required because AIX would currently use the Solaris coding which is not desired. The changes in net_util_md.c fix a potential resource leak and some other code spot was changed where our code base currently has an unnecessary diff.

Thanks for reviewing.

Best regards
Christoph