external/boringssl: Sync to 14308731e5446a73ac2258688a9688b524483cb6.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/ee7aa02744a78bf4630913b1c83d0fe36aa45efc..14308731e5446a73ac2258688a9688b524483cb6

Test: BoringSSL CTS Presubmits.
Change-Id: I73bf80fa018c2a65ca9842f1c2f95d64586bdffc
diff --git a/src/tool/server.cc b/src/tool/server.cc
index 1d6d27c..3b125ad 100644
--- a/src/tool/server.cc
+++ b/src/tool/server.cc
@@ -68,6 +68,9 @@
         "-early-data", kBooleanArgument, "Allow early data",
     },
     {
+        "-tls13-variant", kBooleanArgument, "Enable TLS 1.3 variants",
+    },
+    {
         "", kOptionalArgument, "",
     },
 };
@@ -233,6 +236,11 @@
     SSL_CTX_set_early_data_enabled(ctx.get(), 1);
   }
 
+  // Enabling any TLS 1.3 variant on the server enables all of them.
+  if (args_map.count("-tls13-variant") != 0) {
+    SSL_CTX_set_tls13_variant(ctx.get(), tls13_experiment);
+  }
+
   Listener listener;
   if (!listener.Init(args_map["-accept"])) {
     return false;