fix(esp_http_server): prevent concurrent access to socket used in async http requests (IDFGH-13263)

[fgrfl]

This resolves #13998 with the proposed patch.

With this fix, once a request handler detaches itself from the main http thread with httpd_req_async_handler_begin, the main thread does not read from that socket until the asynchronous handler gives back the session context with httpd_req_async_handler_complete.

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[hmalpani]

Thanks @fgrfl for the PR.

Hello @chipweinberger, can you please take a look at the proposed change?
Thanks!

[chipweinberger]

it's been awhile since i've looked at this code

but looks reasonable

[hmalpani]

sha=4a7f37105659383e154d38d89fbc89cc26e29d9a