move client_auth to handshake

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index d11db3f..69d3b75 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1615,12 +1615,7 @@
     /*
      * PKI layer
      */
-#if defined(MBEDTLS_SSL_CLI_C)
-    int MBEDTLS_PRIVATE(client_auth);           /*!< used to check if CertificateRequest is
-                                                     received from server side. If
-                                                     CertificateReqeust is received, Certificate
-                                                     and CertificateVerify should be sent to server */
-#endif /* MBEDTLS_SSL_CLI_C */
+
     /*
      * User settings
      */