extmod/network_cyw43: Allow configuring active AP interface.

[projectgus]

Summary

Configuring the AP for cyw43 writes to some buffers that are only sent to the modem when the interface is brought up. This means you can't configure the AP after calling active(True), the new settings seem to be accepted but the radio doesn't change.

This is different to the documented WLAN behaviour which says to call active(True) before configuring the interface. The esp8266 and esp32 ports require this, even. EDIT: only esp8266 requires this, esp32 works in either order

Fix this by bouncing the AP interface after a config change, if it's active. Configuring with active(False) still works the same as before.

Adds a static variable to track interface active state, rather than relying on the LWIP interface state. This is because the interface state is updated by a driver callback and there's a race: if code calls active(True) and then config(a=b) then the driver doesn't know it's active yet and the changes aren't correctly applied.

Closes #14224

This work was funded through GitHub Sponsors.

Testing

This is one of two fixes which are required for RPI_PICO_W board to pass the wlan test added in #16225.

Trade-Offs and Alternatives

It is possible this pattern will cause the AP to come up briefly with the default "PICOabcd" SSID before being reconfigured, however (due to the aforementioned race condition) it seems like this may not happen at all before the new config is applied. However, if that was a concern then we could hold off bringing the AP interface up until after it's configured. Doing it that way would be a potential breaking change, though.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.57%. Comparing base (af743ea) to head (181800e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #16226   +/-   ##
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  Coverage   98.57%   98.57%           
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  Files         164      164           
  Lines       21347    21347           
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  Hits        21043    21043           
  Misses        304      304           

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[github-actions]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:   +84 +0.009% RPI_PICO_W[incl +4(bss)]
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:    +0 +0.000% VIRT_RV32

[dpgeorge]

I think the ordering of active(True) vs configuration is quite a tricky issue. If esp32/8266 really do need the interface to be up before it's configured, then won't they always possibly appear briefly as an unconfigured AP first?

IMO for AP it makes sense to first configure everything and then do active(True). If we could make it work that way on esp then I think that would be better.

Regardless of that, this PR is fixing an inconsistency so is probably good to merge it.

[projectgus]

I think the ordering of active(True) vs configuration is quite a tricky issue. If esp32/8266 really do need the interface to be up before it's configured, then won't they always possibly appear briefly as an unconfigured AP first?

Actually I was wrong about esp32, this restriction only exists on esp8266. Will update the commit message and description. esp32 can have active(True) and config() in either order, same as CYW43 (after this commit).

It looks like calling active(True) on the esp8266 without configuring first doesn't result in any AP coming up until you call ap.config() afterward.

[dpgeorge]

Tested on PYBD_SF6, changing the ssid while the AP is active and it does indeed cycle the AP and the new SSID is then visible.