prepare SSL object to work in client or server mode
SSL_CTX object was created with SSL_CTX_new(3), it was either assigned a dedicated client method, a dedicated server method, or a generic method, that can be used for both client and server connections. (The method might have been changed with SSL_CTX_set_ssl_version(3) or SSL_set_ssl_method(3).)When beginning a new handshake, the SSL engine must know whether it must call the connect (client) or accept (server) routines. Even though it may be clear from the method chosen whether client or server mode was requested, the handshake routines must be explicitly set.When using the SSL_connect(3) or SSL_accept(3) routines, the correct handshake routines are automatically set. When performing a transparent negotiation using SSL_write(3) or SSL_read(3), the handshake routines must be explicitly set in advance using either SSL_set_connect_state() or SSL_set_accept_state().