Test that SNI warning alerts are ignored.

Although RFC 6066 recommends against it, some servers send a warning
alert prior to ServerHello on SNI mismatch, and, per spec, TLS 1.2
allows it.

We're fine here, but add a test for it. It interacts interestingly with
TLS 1.3 forbidding warning alerts because it happens before version
negotiation.

Change-Id: I0032313c986c835b6ae1aa43da6ee0dad17a97c2
Reviewed-on: https://boringssl-review.googlesource.com/10800
Reviewed-by: Steven Valdez <svaldez@google.com>
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/ssl/test/runner/runner.go b/ssl/test/runner/runner.go
index 742fb9e..cbb8786 100644
--- a/ssl/test/runner/runner.go
+++ b/ssl/test/runner/runner.go
@@ -2247,6 +2247,15 @@
 				},
 			},
 		},
+		{
+			name: "SendSNIWarningAlert",
+			config: Config{
+				MaxVersion: VersionTLS12,
+				Bugs: ProtocolBugs{
+					SendSNIWarningAlert: true,
+				},
+			},
+		},
 	}
 	testCases = append(testCases, basicTests...)
 }