MINOR: ssl: add prefer-client-ciphers

MINOR: ssl: add prefer-client-ciphers

Currently we unconditionally set SSL_OP_CIPHER_SERVER_PREFERENCE [1],
which may not always be a good thing.

The benefit of server side cipher prioritization may not apply to all
cases out there, and it appears that the various SSL libs are going away
from this recommendation ([2], [3]), as insecure ciphers suites are
properly blacklisted/removed and honoring the client's preference is
more likely to improve user experience  (for example using SW-friendly
ciphers on devices without HW AES support).

This is especially true for TLSv1.3, which will restrict the cipher
suites to just AES-GCM and Chacha20/Poly1305.

Apache [4], nginx [5] and others give admins full flexibility, we should
as well.

The initial proposal to change the current default and add a
"prefer-server-ciphers" option (as implemented in e566ecb) has been
declined due to the possible security impact.

This patch implements prefer-client-ciphers without changing the defaults.

[1] https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html
[2] https://github.com/openssl/openssl/issues/541
[3] https://github.com/libressl-portable/portable/issues/66
[4] https://httpd.apache.org/docs/2.0/en/mod/mod_ssl.html#sslhonorcipherorder
[5] https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_prefer_server_ciphers