RFR: JDK-8306883: Thread stacksize is reported with wrong units in os::create_thread logging

[Thomas Stuefe]

Trivial fix to the display of the thread stack size when UL-logging thread attach.

Before:
`[0.012s][info][os,thread] Thread attached (tid: 153734, pthread id: 139862746482432, stack: 0x00007f3455525000 - 0x00007f3455424000 (1052672k) ).`

Now:
`[0.002s][info][os,thread] Thread attached (tid: 350868, pthread id: 140394443233024, stack: 0x00007fb020eae000 - 0x00007fb020dad000 (1028k) ).`

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Commit messages:
 - JDK-8306883-Thread-stacksize-is-reported-with-wrong-units-in-os-create_thread-logging

Changes: https://git.openjdk.org/jdk/pull/13665/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13665&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306883
  Stats: 4 lines in 4 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/13665.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13665/head:pull/13665

PR: https://git.openjdk.org/jdk/pull/13665