RFR: 8279329: Remove hardcoded IPv4 available policy on Windows

[Masanori Yano]

I added socket connection check same as IPv6_supported().
Before this fix, when IPv4 is uninstalled (called `netsh interface ipv4 uninstall`), and set property `-Djava.net.preferIPv4Stack=true`, java.net.InetAddress.PLATFORM_LOOKUP_POLICY.characteristics is always set to 1(IPv4), because IPv4_supported() always returns TRUE. After applied this fix, java.net.InetAddress.PLATFORM_LOOKUP_POLICY.characteristics is set to 2(IPv6). 
It looks fine that IPv4_supported() returns FALSE.
Would you review this fix?

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Commit messages:
 - 8279329: Remove hardcoded IPv4 available policy on Windows

Changes: https://git.openjdk.java.net/jdk/pull/7317/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7317&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279329
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7317.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7317/head:pull/7317

PR: https://git.openjdk.java.net/jdk/pull/7317