Adding a method to change the initial DTLS retransmission timer value.

This allows an application to override the default of 1 second, which
is what's instructed in RFC 6347 but is not an absolute requirement.

Change-Id: I0bbb16e31990fbcab44a29325b6ec7757d5789e5
Reviewed-on: https://boringssl-review.googlesource.com/7930
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 67a017d..81b34d3 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -148,6 +148,7 @@
     &TestConfig::expect_server_key_exchange_hash },
   { "-expect-key-exchange-info",
     &TestConfig::expect_key_exchange_info },
+  { "-initial-timeout-duration-ms", &TestConfig::initial_timeout_duration_ms },
 };
 
 }  // namespace