RT1744: SSL_CTX_set_dump_dh() doc feedback

The description of when the server creates a DH key is
confusing.  This cleans it up.
(rsalz: also removed trailing whitespace.)

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Merge branch 'master' of git.openssl.org:openssl

Stupid git tricks :(

Reviewed-by: rsalz