Fix and improve SSL_MODE_SEND_FALLBACK_SCSV documentation.

Reviewed-by: NRich Salz <rsalz@openssl.org>

doc/ssl/SSL_CTX_set_mode.pod

@@ -71,12 +71,16 @@ SSL_CTX->freelist_max_len, which defaults to 32.  Using this flag can
 save around 34k per idle SSL connection.
 This flag has no effect on SSL v2 connections, or on DTLS connections.
 
-=item SSL_MODE_FALLBACK_SCSV
+=item SSL_MODE_SEND_FALLBACK_SCSV
 
 Send TLS_FALLBACK_SCSV in the ClientHello.
-To be set by applications that reconnect with a downgraded protocol
+To be set only by applications that reconnect with a downgraded protocol
 version; see draft-ietf-tls-downgrade-scsv-00 for details.
 
+DO NOT ENABLE THIS if your application attempts a normal handshake.
+Only use this in explicit fallback retries, following the guidance
+in draft-ietf-tls-downgrade-scsv-00.
+
 =back
 
 =head1 RETURN VALUES

ssl/ssl.h

@@ -686,8 +686,13 @@ struct ssl_session_st
 #define SSL_MODE_SEND_CLIENTHELLO_TIME 0x00000020L
 #define SSL_MODE_SEND_SERVERHELLO_TIME 0x00000040L
 /* Send TLS_FALLBACK_SCSV in the ClientHello.
- * To be set by applications that reconnect with a downgraded protocol
- * version; see draft-ietf-tls-downgrade-scsv-00 for details. */
+ * To be set only by applications that reconnect with a downgraded protocol
+ * version; see draft-ietf-tls-downgrade-scsv-00 for details.
+ *
+ * DO NOT ENABLE THIS if your application attempts a normal handshake.
+ * Only use this in explicit fallback retries, following the guidance
+ * in draft-ietf-tls-downgrade-scsv-00.
+ */
 #define SSL_MODE_SEND_FALLBACK_SCSV 0x00000080L
 
 /* Cert related flags */