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

internet/stack-ethernet.go

@@ -166,6 +166,14 @@ func (ls *StackEthernet) Encapsulate(carrierData []byte, offsetToIP, offsetToFra
 	*efrm.SourceHardwareAddr() = ls.mac
 	efrm.SetEtherType(ethernet.Type(h.proto))
 	n += 14
+	// Pad to minimum Ethernet frame size (60 bytes without CRC, 64 with).
+	// Frames shorter than this are "runt frames" and may be dropped by switches/routers
+	// according to 802.3 minimum length of 64 octets.
+	const minFrameSize = 60
+	for n < minFrameSize {
+		dst[n] = 0
+		n++
+	}
 	if ls.crcupdate != nil {
 		crc := ls.crcupdate(0, carrierData[offsetToFrame:offsetToFrame+n])
 		binary.LittleEndian.PutUint32(carrierData[offsetToFrame+n:], crc)

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
 }