Bluetooth: Classic: Add length check of user input

[ekleezg]

Added a check for the length of user input as it was missing.

[github-actions]

Hello @ekleezg, and thank you very much for your first pull request to the Zephyr project!
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[jhedberg]

@ekleezg thanks, but no need to split these into multiple commits since they're all quite related to each other. Just squash the changes into a single commit and force push. Also add a commit message body (i.e. some additional text than just the commit subject), since the Compliance CI check will otherwise fail.

[kartben]

@ekleezg you need to amend your git commit author name/email so that it matches the sign-off entry. Thanks!

[ekleezg]

Thank you for let me know. I changed it.

[github-actions]

Hi @ekleezg!
Congratulations on getting your very first Zephyr pull request merged 🎉🥳. This is a fantastic achievement, and we're thrilled to have you as part of our community!

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Thank you for your valuable input, and we look forward to seeing more of your contributions in the future! 🪁