arp: fix runt frames by extending at ethernet level; discard blocking ARP queries after success/failure

x/xnet/stack-blocking.go

@@ -90,11 +90,13 @@ func (s StackBlocking) DoResolveHardwareAddress6(addr netip.Addr, timeout time.D
 		if err == nil {
 			break
 		} else if err = s.checkDeadline(deadline); err != nil {
-			return hw, err
+			break
 		}
 		time.Sleep(sleep)
 		err = errDeadlineExceed // Ensure that if iterations done error is returned.
 	}
+	ip4 := addr.As4()
+	s.async.arp.DiscardQuery(ip4[:])
 	return hw, err
 }