netreg: ignore payload on default case in header build

sys/net/crosslayer/ng_netreg/ng_netreg.c

@@ -152,6 +152,7 @@ ng_pktsnip_t *ng_netreg_hdr_build(ng_nettype_t type, ng_pktsnip_t *payload,
 #endif
 
         default:
+            (void)payload;
             (void)src;
             (void)src_len;
             (void)dst;