encx24j600: add link status support

drivers/encx24j600/encx24j600.c

@@ -401,6 +401,14 @@ static int _get(netdev_t *dev, netopt_t opt, void *value, size_t max_len)
                 res = ETHERNET_ADDR_LEN;
             }
             break;
+        case NETOPT_LINK_CONNECTED:
+            if (reg_get((encx24j600_t *)dev, ENC_ESTAT) & ENC_PHYLNK) {
+                *((netopt_enable_t *)value) = NETOPT_ENABLE;
+            }
+            else {
+                *((netopt_enable_t *)value) = NETOPT_DISABLE;
+            }
+            return sizeof(netopt_enable_t);
         default:
             res = netdev_eth_get(dev, opt, value, max_len);
             break;