Fix transaction propagation

Default transaction's kadcast height cannot be 0.
If so, tx will not be repropagated

pkg/core/mempool/mempool.go

@@ -214,7 +214,12 @@ func (m *Mempool) ProcessTx(srcPeerID string, msg message.Message) ([]bytes.Buff
 		return nil, errors.New("mempool is full, dropping transaction")
 	}
 
-	var h byte
+	// Initializing `h=0` or `h=KadcastInitialHeight` will not work.
+	// This because `h` will be decremented by the kadcast writer as per
+	// it's interpreted as "the kadcast height at which it's been received"
+	// Hence, `h=0` will not be broadcasted at all and
+	// `h=KadcastInitialHeight` will miss the broadcast to the first bucket
+	var h byte = math.MaxUint8
 	if msg.Metadata() != nil {
 		h = msg.Metadata().KadcastHeight
 	}
@@ -495,10 +500,6 @@ func (m Mempool) processGetMempoolTxsBySizeRequest(r rpcbus.Request) (interface{
 
 // kadcastTx (re)propagates transaction in kadcast network.
 func (m *Mempool) kadcastTx(t TxDesc) error {
-	if t.kadHeight > config.KadcastInitialHeight {
-		return errors.New("invalid kadcast height")
-	}
-
 	/// repropagate
 	buf := new(bytes.Buffer)
 	if err := transactions.Marshal(buf, t.tx); err != nil {