ESP8266 Drv support baud-rate switch

[cyliangtw]

Summary of changes

ESP8266 WiFi module default baud-rate is 115200, this PR is to support the baud-rate switch from default baud-rate to the target baud-rate.

Documentation

None

Pull request type

[v] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[v] Tests / results supplied as part of this PR

test-log.txt

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Reviewers

@michalpasztamobica

[0xc0170]

Please fix the style issue

[michalpasztamobica]

Hi @cyliangtw . We are already calling AT+UART_CUR on startup in stop_uart_hw_flow_ctrl(). This is also visible in the logs you attached...
Can you please explain how this PR improves the current behavior?

[ciarmcom]

@cyliangtw, thank you for your changes.
@michalpasztamobica @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[cyliangtw]

@michalpasztamobica, if some platform not support flow control, stop_uart_hw_flow_ctrl() will not work.
More, if the original instructor set serial obj baud != 115200, later _parser.send() can't communicate with wifi module caused by the un-matching baud-rate.

[michalpasztamobica]

Thanks for the explanation. This makes sense to me now and I also verified that actually setting baud rate different than default did not work and the code on your branch fixes the issue.

Thanks a lot for this contribution!

[michalpasztamobica]

Fixes #12710

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 6 of 6 test jobs passed
Build number : 1
Build artifacts