Documentation | Update B0 baud rate handling in POSIX Users Guide (#170)

[SHIVAM DEOLANKAR (@D3athSkulll)]

Issue created by SHIVAM DEOLANKAR: https://gitlab.rtems.org/rtems/docs/rtems-docs/-/work_items/170



## Summary

The termios implementation does not support output baud rate B0 when configuring device attributes through `tcsetattr()`.

Document that requests to set the output baud rate to B0 fail with `ENOTSUP`, since the corresponding hangup operation is not supported by the termios device configuration interface.

Update the relevant POSIX Users Guide documentation accordingly.

This is the [URL](https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/termios.h.html) for Baud Rate functions from termios.h documentation which should be referenced .

## Steps to reproduce

<!--Pre-set options
- milestone-->

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/docs/rtems-docs/-/work_items/170
You're receiving this email because of your account on gitlab.rtems.org. Unsubscribe from this thread: https://gitlab.rtems.org/-/namespace/19/sent_notifications/6-8ge37s88uvjptxeh150bkabpt-j/unsubscribe | Manage all notifications: https://gitlab.rtems.org/-/profile/notifications | Help: https://gitlab.rtems.org/help


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/bugs/attachments/20261109/687b2ddc/attachment.htm>