Technically an API break

[Matt Caswell]

PR11589 makes a change to the public API function
`SSL_set_record_padding_callback` to change its return type from void to
int:

https://github.com/openssl/openssl/pull/11589

This is technically an API break - but it doesn't seem too serious. It's
possible, I suppose, that existing applications that use this will fail
to spot the error return since this function can now fail. The function
itself was only recently added (in 1.1.1), and I suspect real-world
usage is very small (or possibly nil).

Is this considered ok?

Matt