ng_ndp: fix _get_l2src

sys/net/network_layer/ng_ndp/ng_ndp.c

@@ -636,24 +636,28 @@ static uint16_t _get_l2src(uint8_t *l2src, size_t l2src_size, kernel_pid_t iface
     bool try_long = false;
     int res;
     uint16_t l2src_len;
+    /* maximum address length that fits into a minimum length (8) S/TL2A option */
+    const uint16_t max_short_len = 6;
 
     /* try getting source address */
     if ((ng_netapi_get(iface, NETCONF_OPT_SRC_LEN, 0, &l2src_len,
                        sizeof(l2src_len)) >= 0) &&
-        (l2src_len == 8)) {
+        (l2src_len > max_short_len)) {
         try_long = true;
     }
 
-    if ((try_long && ((res = ng_netapi_get(iface, NETCONF_OPT_ADDRESS_LONG, 0,
-                                           l2src, l2src_size)) < 0)) ||
-        ((res = ng_netapi_get(iface, NETCONF_OPT_ADDRESS, 0, l2src,
-                              l2src_size)) < 0)) {
-        DEBUG("ndp: no link-layer address found.\n");
-        l2src_len = 0;
+    if (try_long && ((res = ng_netapi_get(iface, NETCONF_OPT_ADDRESS_LONG, 0,
+                                          l2src, l2src_size)) > max_short_len)) {
+        l2src_len = (uint16_t)res;
     }
-    else {
+    else if ((res = ng_netapi_get(iface, NETCONF_OPT_ADDRESS, 0, l2src,
+                                  l2src_size)) >= 0) {
         l2src_len = (uint16_t)res;
     }
+    else {
+        DEBUG("ndp: no link-layer address found.\n");
+        l2src_len = 0;
+    }
 
     return l2src_len;
 }