Implement a (bounded) buffer of request body data to provide a limited

Implement a (bounded) buffer of request body data to provide a limited
but safe fix for the mod_ssl renegotiation-vs-requests-with-bodies
bug:

* modules/ssl/ssl_private.h (ssl_io_buffer_fill): Add prototype.

* modules/ssl/ssl_engine_io.c (ssl_io_buffer_fill,
ssl_io_filter_buffer): New functions.

* modules/ssl/ssl_engine_kernel.c (ssl_hook_Access): If a
renegotiation is needed, and the request has a non-zero
content-length, or a t-e header (and 100-continue was not requested),
call ssl_io_buffer_fill to set aside the request body data if
possible, then proceed with the negotiation.

PR: 12355

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@290965 13f79535-47bb-0310-9956-ffa450edef68