When wolfSSL_SetVersion() is called to set a specific TLS version,
the downgrade flag is now set to 0. This causes wolfSSL_parse_cipher_list()
to no longer preserve cipher suites from the other TLS version group.
Previously, when using SSLv23 method and setting cipher suites for only
one TLS version (e.g., TLS 1.2), the library would preserve any existing
cipher suites from the other version (e.g., TLS 1.3) for OpenSSL API
compatibility. With this change, if a specific version is set via
wolfSSL_SetVersion(), only the cipher suites for that version are kept.