Add wait flight2 state.

The state is come from RFC8446 section A.2

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 3c2696f..2bca21a 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -687,12 +687,12 @@
     MBEDTLS_SSL_SERVER_FINISHED,
     MBEDTLS_SSL_FLUSH_BUFFERS,
     MBEDTLS_SSL_HANDSHAKE_WRAPUP,
-
     MBEDTLS_SSL_NEW_SESSION_TICKET,
     MBEDTLS_SSL_SERVER_HELLO_VERIFY_REQUEST_SENT,
     MBEDTLS_SSL_HELLO_RETRY_REQUEST,
     MBEDTLS_SSL_ENCRYPTED_EXTENSIONS,
     MBEDTLS_SSL_END_OF_EARLY_DATA,
+    MBEDTLS_SSL_WAIT_FLIGHT2,
     MBEDTLS_SSL_CLIENT_CERTIFICATE_VERIFY,
     MBEDTLS_SSL_CLIENT_CCS_AFTER_SERVER_FINISHED,
     MBEDTLS_SSL_CLIENT_CCS_BEFORE_2ND_CLIENT_HELLO,