Make header references conform with man-pages(7) in all manuals

Make header references conform with man-pages(7) in all manuals

Details from man-pages(7) that are used:

   Formatting conventions (general)

       ...
       Filenames (whether pathnames, or references to header files) are always
       in italics (e.g., <stdio.h>), except in the SYNOPSIS section, where in‐
       cluded files are in bold (e.g., #include <stdio.h>).  When referring to
       a standard header file include, specify the header file  surrounded  by
       angle brackets, in the usual C way (e.g., <stdio.h>).
       ...

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/13843)