Add a test for RSA ServerKeyExchange.

Ensure that the client rejects it with UNEXPECTED_MESSAGE, not by attempting to
decode it.

Change-Id: Ifc5613cf1152e0f7dcbee73e05df1ef367dfbfd5
Reviewed-on: https://boringssl-review.googlesource.com/2232
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/runner/common.go b/ssl/test/runner/common.go
index 8cdbaea..c77f765 100644
--- a/ssl/test/runner/common.go
+++ b/ssl/test/runner/common.go
@@ -505,6 +505,10 @@
 	// stress the replay bitmap window by simulating extreme packet loss and
 	// retransmit at the record layer.
 	SequenceNumberIncrement uint64
+
+	// RSAServerKeyExchange, if true, causes the server to send a
+	// ServerKeyExchange message in the plain RSA key exchange.
+	RSAServerKeyExchange bool
 }
 
 func (c *Config) serverInit() {