Adding TLS 1.3 constants.

Constants representing TLS 1.3 are added to allow for future work to be
flagged on TLS1_3_VERSION. To prevent BoringSSL from negotiating the
non-existent TLS 1.3 version, it is explicitly disabled using
SSL_OP_NO_TLSv1_3.

Change-Id: Ie5258a916f4c19ef21646c4073d5b4a7974d6f3f
Reviewed-on: https://boringssl-review.googlesource.com/8041
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index bd583e8..1648922 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -537,6 +537,7 @@
 #define TLS1_VERSION 0x0301
 #define TLS1_1_VERSION 0x0302
 #define TLS1_2_VERSION 0x0303
+#define TLS1_3_VERSION 0x0304
 
 #define DTLS1_VERSION 0xfeff
 #define DTLS1_2_VERSION 0xfefd
@@ -3230,6 +3231,7 @@
 #define SSL_OP_NO_TLSv1 0x04000000L
 #define SSL_OP_NO_TLSv1_2 0x08000000L
 #define SSL_OP_NO_TLSv1_1 0x10000000L
+#define SSL_OP_NO_TLSv1_3 0x20000000L
 #define SSL_OP_NO_DTLSv1 SSL_OP_NO_TLSv1
 #define SSL_OP_NO_DTLSv1_2 SSL_OP_NO_TLSv1_2
 
@@ -3386,6 +3388,7 @@
 #define SSL_TXT_TLSV1 "TLSv1"
 #define SSL_TXT_TLSV1_1 "TLSv1.1"
 #define SSL_TXT_TLSV1_2 "TLSv1.2"
+#define SSL_TXT_TLSV1_3 "TLSv1.3"
 #define SSL_TXT_ALL "ALL"
 #define SSL_TXT_CMPDEF "COMPLEMENTOFDEFAULT"