MINOR: ssl: set SSL_OP_PRIORITIZE_CHACHA

MINOR: ssl: set SSL_OP_PRIORITIZE_CHACHA

Sets OpenSSL 1.1.1's SSL_OP_PRIORITIZE_CHACHA unconditionally, as per [1]:

When SSL_OP_CIPHER_SERVER_PREFERENCE is set, temporarily reprioritize
ChaCha20-Poly1305 ciphers to the top of the server cipher list if a
ChaCha20-Poly1305 cipher is at the top of the client cipher list. This
helps those clients (e.g. mobile) use ChaCha20-Poly1305 if that cipher
is anywhere in the server cipher list; but still allows other clients to
use AES and other ciphers. Requires SSL_OP_CIPHER_SERVER_PREFERENCE.

[1] https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_clear_options.html