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

[robert engels]

fix bug JDK-B6968351 by avoiding flush after response headers

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Commit messages:
 - remove extraneous whitespace change
 - fix for small messages with tcp_nodelay off

Changes: https://git.openjdk.org/jdk/pull/18667/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18667&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6968351
  Stats: 104 lines in 3 files changed: 97 ins; 4 del; 3 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