Add Data-less Zero-RTT support.

This adds support on the server and client to accept data-less early
data. The server will still fail to parse early data with any
contents, so this should remain disabled.

BUG=76

Change-Id: Id85d192d8e0360b8de4b6971511b5e8a0e8012f7
Reviewed-on: https://boringssl-review.googlesource.com/12921
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/tool/server.cc b/tool/server.cc
index 20c913c..1a97dff 100644
--- a/tool/server.cc
+++ b/tool/server.cc
@@ -54,6 +54,9 @@
         "The server will continue accepting new sequential connections.",
     },
     {
+        "-early-data", kBooleanArgument, "Allow early data",
+    },
+    {
         "", kOptionalArgument, "",
     },
 };
@@ -223,6 +226,10 @@
     return false;
   }
 
+  if (args_map.count("-early-data") != 0) {
+    SSL_CTX_set_early_data_enabled(ctx.get(), 1);
+  }
+
   bool result = true;
   do {
     int sock = -1;