wallet/rpc: Use the default maxfeerate value as BTC/kB

test/functional/mempool_accept.py

@@ -183,6 +183,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
         self.check_mempool_result(
             result_expected=[{'txid': tx.rehash(), 'allowed': True}],
             rawtxs=[tx.serialize().hex()],
+            maxfeerate=0,
         )
 
         self.log.info('A transaction with no outputs')