add enable/disable radio promiscuous mode method and simulated posix … (#84)

* add enable/disable radio promiscuous mode method and simulated posix radio that supports promiscuous mode

* fix code style

include/platform/radio.h

@@ -277,6 +277,21 @@ int8_t otPlatRadioGetNoiseFloor(void);
  */
 otRadioCaps otPlatRadioGetCaps(void);
 
+/**
+ * Enable or disable promiscuous mode.
+ *
+ * @param[in]  aEnable  A value to enable or disable promiscuous mode.
+ */
+void otPlatRadioSetPromiscuous(bool aEnable);
+
+/**
+ * Get the status of promiscuous mode.
+ *
+ * @retval ::true          The promiscuous mode is enabled.
+ * @retval ::false         The promiscuous mode is disabled.
+ */
+bool otPlatRadioGetPromiscuous(void);
+
 /**
  * @}
  *