kw2xrf: Add NETOPT_CHANNEL to getters

drivers/kw2xrf/kw2xrf_netdev.c

@@ -318,6 +318,13 @@ int _get(netdev_t *netdev, netopt_t opt, void *value, size_t len)
                 !!(dev->netdev.flags & KW2XRF_OPT_AUTOCCA);
             return sizeof(netopt_enable_t);
 
+        case NETOPT_CHANNEL:
+            if (len < sizeof(uint16_t)) {
+                return -EOVERFLOW;
+            }
+            *((uint16_t *)value) = kw2xrf_get_channel(dev);
+            return sizeof(uint16_t);
+
         case NETOPT_TX_POWER:
             if (len < sizeof(int16_t)) {
                 return -EOVERFLOW;