Add a note about aborts encountered while sending early_data

In some circumstances it is possible for a client to have a session
reporting a max early data value that is greater than the server will
support. In such cases the client could encounter an aborted connection.

Fixes #6735

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/6740)