RFR: 8323122: AArch64: Increase itable stub size estimate

[Yude Lin]

Since [JDK-8307352](https://bugs.openjdk.org/browse/JDK-8307352), itable stub size has grown by 20 bytes on linux-aarch64. In particular, the "slop-counted" code increases from 100->120 bytes, where the current estimate is 124 bytes. I haven't found a case where it exceeds the estimate. For now this size is stable across the few linux-aarch64 configurations I ran with. It doesn't vary (for example) by different klass decoding schemes. But I think the idea of the estimate is that we can never know. I propose we increase the estimate to be safe.

Passed hotspot/jtreg/:tier1

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Commit messages:
 - 8323122: AArch64: Increase itable stub size estimate

Changes: https://git.openjdk.org/jdk/pull/17336/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17336&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323122
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17336.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17336/head:pull/17336

PR: https://git.openjdk.org/jdk/pull/17336