[#239] morph/client: Simplify code interacting with magic numbers

It can't be uint64 in fact, but this error is buried deeply in the NetworkInfo
API structure, so we're not touching MagicNumber() for now.

Signed-off-by: Roman Khimov <roman@nspcc.ru>
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/morph/client/notary.go

@@ -412,16 +412,11 @@ func (c *Client) NotarySignAndInvokeTX(mainTx *transaction.Transaction) error {
 		return err
 	}
 
-	// error appears only if client
-	// is in inactive mode; that has
-	// been already checked above
-	magicNumber, _ := c.MagicNumber()
-
 	// mainTX is expected to be pre-validated: second witness must exist and be empty
 	mainTx.Scripts[1].VerificationScript = multiaddrAccount.GetVerificationScript()
 	mainTx.Scripts[1].InvocationScript = append(
 		[]byte{byte(opcode.PUSHDATA1), 64},
-		multiaddrAccount.PrivateKey().SignHashable(uint32(magicNumber), mainTx)...,
+		multiaddrAccount.SignHashable(c.rpcActor.GetNetwork(), mainTx)...,
 	)
 
 	//lint:ignore SA1019 https://git.frostfs.info/TrueCloudLab/frostfs-node/issues/202
@@ -667,12 +662,12 @@ func (c *Client) notaryWitnesses(invokedByAlpha bool, multiaddr *wallet.Account,
 	// to pass Notary module verification
 	var invokeScript []byte
 
-	magicNumber, _ := c.MagicNumber()
+	magicNumber := c.rpcActor.GetNetwork()
 
 	if invokedByAlpha {
 		invokeScript = append(
 			[]byte{byte(opcode.PUSHDATA1), 64},
-			multiaddr.PrivateKey().SignHashable(uint32(magicNumber), tx)...,
+			multiaddr.SignHashable(magicNumber, tx)...,
 		)
 	} else {
 		// we can't provide alphabet node signature
@@ -694,7 +689,7 @@ func (c *Client) notaryWitnesses(invokedByAlpha bool, multiaddr *wallet.Account,
 		// then we have invoker witness
 		invokeScript = append(
 			[]byte{byte(opcode.PUSHDATA1), 64},
-			c.acc.PrivateKey().SignHashable(uint32(magicNumber), tx)...,
+			c.acc.SignHashable(magicNumber, tx)...,
 		)
 
 		w = append(w, transaction.Witness{