RFR: 8255999: Shenandoah: Invoke native-LRB only on non-strong refs, again [v2]

[Roman Kennke]

> In JDK-8255691, I changed the condition for invoking native-LRB only on non-strong-refs. Somehow, when merging JDK-8254315, I got the condition wrong again. 
> 
> Testing: hotspot_gc_shenandoah

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8255999
 - 8255999: Shenandoah: Invoke native-LRB only on non-strong refs, again

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1101/files
  - new: https://git.openjdk.java.net/jdk/pull/1101/files/b552dc70..20f503a8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1101&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1101&range=00-01

  Stats: 46846 lines in 372 files changed: 25991 ins; 13585 del; 7270 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1101.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1101/head:pull/1101

PR: https://git.openjdk.java.net/jdk/pull/1101