Merge pull request #4848 from haukepetersen/fix_nrf51dongle_xtimer

boards/nrf51dongle: add xtimer configuration

boards/nrf51dongle/include/board.h

@@ -28,6 +28,17 @@
 extern "C" {
 #endif
 
+/**
+ * @brief   Xtimer configuration
+ * @{
+ */
+#define XTIMER                      (0)
+#define XTIMER_CHAN                 (0)
+#define XTIMER_MASK                 (0xff000000)
+#define XTIMER_SHIFT_ON_COMPARE     (2)
+#define XTIMER_BACKOFF              (40)
+/** @} */
+
 /**
  * @name    LED pin definitions
  * @{