make it call etharp_output_sent() in tapif_output.This is to prevent the recently

discovered memory leak.

src/arch/unix/netif/tapif.c

@@ -262,6 +262,8 @@ tapif_output(struct netif *netif, struct pbuf *p,
   p = etharp_output(netif, ipaddr, p);
   if(p != NULL) {
     return low_level_output(netif, p);
+    etharp_output_sent(p);
+    p = NULL;
   }
   return ERR_OK;
 }