add description of -no_ecdhe option to s_server man page
add description of -no_ecdhe option to s_server man page

While the -help message references this option, the man page
doesn't mention the -no_ecdhe option.
This patch fixes this omission.

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