RFR: 6968351: httpserver clashes with delayed TCP ACKs for low Content-Length [v3]

[robert engels]

> fix bug JDK-B6968351 by avoiding flush after response headers

robert engels has updated the pull request incrementally with two additional commits since the last revision:

 - automatically close a fixed response. this is benign as a further close is ignore, and a further write continues to throw an exception for too much data
 - update based on PR review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18667/files
  - new: https://git.openjdk.org/jdk/pull/18667/files/8aa89b0d..c5f26ada

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18667&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18667&range=01-02

  Stats: 11 lines in 2 files changed: 7 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18667.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18667/head:pull/18667

PR: https://git.openjdk.org/jdk/pull/18667