Implement Smart Config for ESP32

[mikee47]

Re. #2473 here are the bones of a smart config implementation for ESP32.

TODO:

• Fix missing __wrap_putchar error (libsc_get_ssid_passwd.a)
• Test

Closes #2473

[kmihaylov]

Ah I missed it :)
kmihaylov@94dc8fa
I got lost with std::unique_ptr so I took a rest and here you already made it...

Anyway, I'll be glad to tell me how Sming includes the esp-idf header files?

[mikee47]

The Basic_SmartConfig sample kind of works, with a couple of provisos:

Smart config won't work if station has already been configured and set to auto-connect on startup.
Error is STA is connecting, scan are not allowed!.
This is perfectly logical and probably something the applicatdion should address rather than the framework.
i.e. need to call WifiStation.disconnect() first.

Attempting to configure with wrong credentials isn't really handled. Again, that's something the application needs to consider. I took a quick look at ESP8266 behaviour and same deal.

[mikee47]

Note: The __wrap_putchar doesn't seem to get called, no idea what it's for...

UPDATE: My bad, typo in libc, now fixed :-)

[kmihaylov]

Works well for me. Both the example and in my project.
Great work @mikee47 !

[mikee47]

Refinement to the event handling now blocks auto-connect if WPS or SmartConfig are active, so the Basic_SmartConfig sample works even if already configured.