RFR: 8282917: Remove InetAddressImplFactory from InetAddress [v2]

[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

Aleksei Efimov has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7842/files
  - new: https://git.openjdk.java.net/jdk/pull/7842/files/0af45a2d..49fdd576

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7842&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7842&range=00-01

  Stats: 6 lines in 1 file changed: 0 ins; 4 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