Add handlers for parameter validation in the sample programs

The sample programs require an additional handler function of
mbedtls_param_failed() to handle any failed parameter validation checks enabled
by the MBEDTLS_CHECK_PARAMS config.h option.
diff --git a/programs/ssl/mini_client.c b/programs/ssl/mini_client.c
index 290455e..c447947 100644
--- a/programs/ssl/mini_client.c
+++ b/programs/ssl/mini_client.c
@@ -168,6 +168,14 @@
     ssl_write_failed,
 };
 
+#if defined( MBEDTLS_CHECK_PARAMS ) && defined(MBEDTLS_PLATFORM_C)
+void mbedtls_param_failed( char* failure_condition, char* file, int line )
+{
+    mbedtls_printf("%s:%i: Input param failed - %sn", file, line,                           failure_condition );
+    mbedtls_exit( MBEDTLS_EXIT_FAILURE );
+}
+#endif
+
 int main( void )
 {
     int ret = exit_ok;