use maxint-2 to signal RBF, in order to standardize with Bitcoin Core

lib/transaction.py

@@ -681,9 +681,10 @@ class Transaction:
         s += int_to_hex(txin.get('sequence', 0xffffffff), 4)
         return s
 
-    def set_sequence(self, n):
+    def set_rbf(self, rbf):
+        nSequence = 0xffffffff - (2 if rbf else 0)
         for txin in self.inputs():
-            txin['sequence'] = n
+            txin['sequence'] = nSequence
 
     def BIP_LI01_sort(self):
         # See https://github.com/kristovatlas/rfc/blob/master/bips/bip-li01.mediawiki