Rename XXX_SINGLE_CIPHERSUITE -> XXX_CONF_SINGLE_CIPHERSUITE

This is in line with the other configurations options used
to hardcoded aspects of the SSL configuration.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index f4d51dc..8774003 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1816,7 +1816,7 @@
      * Initialize update checksum functions
      */
     server_suite_info = mbedtls_ssl_ciphersuite_from_id( i );
-#if !defined(MBEDTLS_SSL_SINGLE_CIPHERSUITE)
+#if !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE)
     ssl->handshake->ciphersuite_info = server_suite_info;
 #endif
     if( server_suite_info == MBEDTLS_SSL_CIPHERSUITE_INVALID_HANDLE )
@@ -1874,9 +1874,9 @@
 #if defined(MBEDTLS_HAVE_TIME)
         ssl->session_negotiate->start = mbedtls_time( NULL );
 #endif
-#if !defined(MBEDTLS_SSL_SINGLE_CIPHERSUITE)
+#if !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE)
         ssl->session_negotiate->ciphersuite = i;
-#endif /* MBEDTLS_SSL_SINGLE_CIPHERSUITE */
+#endif /* MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE */
         ssl->session_negotiate->compression = comp;
         ssl->session_negotiate->id_len = n;
         memcpy( ssl->session_negotiate->id, buf + 35, n );