pass up a RADIO_NOACK to the MAC layer.

core/dev/radio.h

@@ -96,6 +96,7 @@ enum {
   RADIO_TX_OK,
   RADIO_TX_ERR,
   RADIO_TX_COLLISION,
+  RADIO_TX_NOACK,
 };
 
 #endif /* __RADIO_H__ */

core/net/mac/nullrdc.c

@@ -171,6 +171,9 @@ send_packet(mac_callback_t sent, void *ptr)
     case RADIO_TX_COLLISION:
       ret = MAC_TX_COLLISION;
       break;
+    case RADIO_TX_NOACK:
+      ret = MAC_TX_NOACK;
+      break;
     default:
       ret = MAC_TX_ERR;
       break;