HDDS-15772. Stop forcing java.net.preferIPv4Stack=true for Ozone daemons and tests

[echonesis]

What changes were proposed in this pull request?

Ozone currently forces java.net.preferIPv4Stack=true for daemon processes and Maven test executions.
This prevents the JVM from using its default networking behavior and blocks IPv6-capable or dual-stack environments unnecessarily.

• Removes the default java.net.preferIPv4Stack=true setting from Ozone shell bootstrap.
• Removes the corresponding global Surefire system property.
• Removes the legacy Linux net.ipv6.bindv6only check and the undocumented OZONE_ALLOW_IPV6 developer override.
• Updates ozone-env.sh to document that Ozone follows the JVM's default IP stack preference while retaining instructions for operators who need to force IPv4.
• Adds Bats coverage verifying that shell bootstrap does not force IPv4 by default and preserves an explicitly configured IPv4 preference.

Operators can continue to force IPv4 when required by setting:

export OZONE_OPTS="-Djava.net.preferIPv4Stack=true"

Generated-by: Codex (GPT-5)

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15772

How was this patch tested?

GitHub Actions CI: https://github.com/echonesis/ozone/actions/runs/29590987895