Adds missing `CONFIG_BT_NIMBLE_ENABLED` check

[abrondijk]

Description

Closes https://github.com/esp-cpp/espp/issues/238.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update
• [ ] Hardware (schematic, board, system design) change
• [ ] Software change

[github-actions[bot]]

:white_check_mark:Static analysis result - no issues found! :white_check_mark: