doc: smp: Wrong body length in SMP UART transport

[nordicjm]

Describe the bug
The length wrong says MTU - 3 instead of MTU - 5 on the SMP UART transport page

[henrikbrixandersen]

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[nordicjm]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.md

Did not bother as it's a backport of a doc fix.

[nashif]

Did not bother as it's a backport of a doc fix.

tbh, I'd rather merge such a doc fix without an issue and not deal with bug reports like this, this bug report does not have the minimal language required to understand what is going on here, where is the issue, what file, what is the context? smp? Is this symmetric multi processing maybe?

This issue eventually will be linked into release notes, someone who wants to know how changes might impact them upgrading to 3.7.1 might open this to see what is the context and what is the bug being fixed. Lacking the basic information of where the bug is and its impact might leave someone wondering.

[nordicjm]

Are we ok to open/backport doc-only changes without an issue? I opened this to avoid the CI failure with needing an issue. There was no bug in the code at all, just in the documentation a part had 3 bytes instead of 5. I wouldn't expect this to part of the changelog