Fix variable names with modname in module Makefile

[simayosi]

Proposed changes

In Makefile.module-*, variable names should use underscores (_) instead of dashes (-) in module names.
This convention is followed in code such as alpine/Makefile:114 and debian/Makefile:116.
For example, the version variable for the headers-more module in Makefile.headers-more is defined asMODULE_VERSION_headers_more.

However, build_module.sh currently generates Makefile.module-$MODULE_NAME using the module name as-is in variable names, without converting dashes to underscores.
As a result, modules with dashes in their names cannot be built correctly.

This patch addresses the issue by ensuring that module names used in variable names have dashes replaced with underscores.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant tests pass after adding my changes.
• I have updated any relevant documentation (README.md and/or CHANGELOG.md).