DO NOT MERGE (ARROW-16218: [Java] Don't depend on netty-transport-native-unix-common on s390x)

[pitrou]

PR created only to get a Travis-CI build for #12913

[github-actions[bot]]

Thanks for opening a pull request!

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ARROW-${JIRA_ID}: [${COMPONENT}] ${SUMMARY}

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• Other pull requests
• Contribution Guidelines - How to contribute patches

[amol-]

Closing because it has been untouched for a while, in case it's still relevant feel free to reopen and move it forward 👍