[FS#589] curl --capath not supported on mbedtls but was supported on polarssl

[LEDE Bugs]

The following task has a new comment added:

FS#589 - curl --capath not supported on mbedtls but was supported on polarssl
User who did this - Federico Capoano (nemesisdesign)

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I found a workaround that seems to work and maintain backward compatibility with older OpenWRT versions:
https://github.com/openwisp/openwisp-config/commit/5c4f214946ce713d6e7e6ecf2f0479b8d21ed484

I hope is not too heretic.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=589#comment2172