Reenable s_server -dhparam option
Reenable s_server -dhparam option

This option was lost when converting to a table-driven option parser
in commit 7e1b7485706c2b11091b5fa897fe496a2faa56cc.

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4398)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl