doc: Add note for Class C device

[i3mSuperMan]

Summary

When the support class c option is enabled for an active device, the changes will take effect after the device re-join the network (OTAA) or on device reset (ABP). Added a note to make it clear to the users on this behavior.

Screenshots

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Changes

Added the below point as a note.

For an active device, if you enable the supports-class-c option, the setting will take effect after OTAA join or ABP FCnt reset, ResetInd, or after MAC state reset. So, please ensure to re-join a device after you have enabled the supports-class-c option.

Notes for Reviewers

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Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Run Locally: Verified that the docs build using make server, posted screenshots, verified external links. Test with HUGO_PARAMS_SEARCH_ENABLED=true if style changes will affect the search bar.
• New Features Marked: Documentation for new features is marked using the new-in-version shortcode, according to the guidelines in CONTRIBUTING.
• Style Guidelines: Documentation obeys style guidelines in CONTRIBUTING.
• Commits: Commit messages follow guidelines in CONTRIBUTING, there are no fixup commits left.