Make function mbedtls_ssl_set_hostname(...) as optional

Now function mbedtls_ssl_set_hostname is compile-time configurable
in config.h with define MBEDTLS_X509_REMOVE_HOSTNAME_VERIFICATION.
This affects to many x509 API's. See config.h for details.
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index a7fd259..2aa4950 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -2053,7 +2053,7 @@
         goto exit;
     }
 
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#if defined(MBEDTLS_X509_CRT_PARSE_C) && !defined(MBEDTLS_X509_REMOVE_HOSTNAME_VERIFICATION)
     if( ( ret = mbedtls_ssl_set_hostname( &ssl, opt.server_name ) ) != 0 )
     {
         mbedtls_printf( " failed\n  ! mbedtls_ssl_set_hostname returned %d\n\n",