doc/man3: use the documented coding style in the example code

Adjust brace placement, whitespace after keywords, indentation and empty
lines after variable declarations according to
https://www.openssl.org/policies/codingstyle.html

.

Indent literal sections by exactly one space.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1956)