[jdk11u-dev] RFR: 8305906: HttpClient may use incorrect key when finding pooled HTTP/2 connection for IPv6 address

[Tyler Steele]

This PR backports the change reported in [JDK-8305906](https://bugs.openjdk.org/browse/JDK-8305906).

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Commit messages:
 - Backport 3ccb3c0e09f9a414229d3f76031f3fc8f271c936

Changes: https://git.openjdk.org/jdk11u-dev/pull/1941/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1941&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305906
  Stats: 194 lines in 3 files changed: 183 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1941.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/1941/head:pull/1941

PR: https://git.openjdk.org/jdk11u-dev/pull/1941