RFR: 8272996: JNDI DNS provider fails to resolve SRV entries when IPV6 stack is enabled

[Aleksei Efimov]

Hi,

JNDI's `DnsClient` can fail with `UncheckedIOException` during `connect` or `disconnect` method calls. It is a [know behavior](https://bugs.openjdk.java.net/browse/JDK-8236076) of `DatagramSocket`.

Currently, `DnsClient` method is fast-fails when `UncheckedIOException` is observed during connect attempt. But it supposed to mark such server as invalid and continue checking other servers.

Testing: tier1, tier2, tier3 and existing JCK tests show no failures relevant to the proposed changed

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Commit messages:
 - 8272996: JNDI DNS provider fails to resolve SRV entries when IPV6 stack is enabled

Changes: https://git.openjdk.java.net/jdk/pull/7353/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7353&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272996
  Stats: 19 lines in 1 file changed: 11 ins; 6 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7353.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7353/head:pull/7353

PR: https://git.openjdk.java.net/jdk/pull/7353