RFR: 8282917: Remove InetAddressImplFactory from InetAddress

[Aleksei Efimov]

Hi,

This cleanup change removes `InetAddressImplFactory` class from `InetAddress`. The list of changes:
- Remove `InetAddressImplFactory` from `InetAddress`
- Since `isIPv6Supported` native code is identical for Windows and Unix implementations it was moved to the libnet's `InetAddress.c`.
- `InetAddressImplFactory.c` Windows and Unix implementations were removed

Testing: jdk-tier1 to jdk-tier3 tests show no failures related to the change

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Commit messages:
 - Merge branch 'master' into JDK-8282917_Remove_InetAddressImplFactory
 - 8282917: Remove InetAddressImplFactory from InetAddress

Changes: https://git.openjdk.java.net/jdk/pull/7842/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7842&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282917
  Stats: 125 lines in 4 files changed: 18 ins; 105 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7842.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7842/head:pull/7842

PR: https://git.openjdk.java.net/jdk/pull/7842