RFR: 8253118: Avoid unnecessary deopts when OSR nmethods of the same level are present.

[Igor Veresov]

When running with ```-XX:TieredStopAtLevel={2|3}``` the policy tried to switch to OSR method of the same level if those
are present, which caused constant deopting. The fix is to consider only higher levels for OSR switches.

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Commit messages:
 - Prevent switching to same level OSR.

Changes: https://git.openjdk.java.net/jdk/pull/360/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=360&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253118
  Stats: 9 lines in 1 file changed: 3 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/360.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/360/head:pull/360

PR: https://git.openjdk.java.net/jdk/pull/360