add ESP8266 interface suspend and resume APIs

[soleilplanet]

Summary of changes

Add and expose ESP8266 interface suspend and resume APIs to allow user applications to perform power management control with deep sleep

Impact of changes

New APIs exposed to enable/disable traffic over ESP8266 input or output interface

Migration actions required

N/A

Documentation

Need to add the API descriptions of the interface_suspend() and interface_resume()

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] 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

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

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Reviewers

@kjbracey-arm

[ciarmcom]

@soleilplanet, thank you for your changes.
@kjbracey-arm @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

@soleilplanet please fix the astyle errors

[0xc0170]

suspend/resume wouldn't be sufficient (no need for interface_) ? I dont see it defined anywhere in Mbed OS codebase as it is here

[soleilplanet]

well I put the interface_ here because I don't want to confuse the users. The API is not to suspend/resume the ESP8266 itself, but only the traffic.
But on second thought, the class itself is ESP8266Interface, so perhaps it wouldn't confuse users. How do you think?

[adbridge]

@0xc0170 can you answer the questions please? @ARMmbed/mbed-os-ipcore could someone review this ?

[michalpasztamobica]

@soleilplanet , with this PR we enabled deep sleep whenever ESP gets disconnected. I think this API extension is not needed.

[0xc0170]

@soleilplanet , with this PR we enabled deep sleep whenever ESP gets disconnected. I think this API extension is not needed.

Based on this, I'll close the PR. If it's not correct, please let us know or just reopen the PR with a reason.