test: add option to speed up tx relay/mempool sync

when `self.noban_tx_relay=True`, the following flag
`-whitelist=noban,in,out@127.0.0.1`is added to `extra_args`
to speed up tx relay/mempool sync.

test/functional/rpc_rawtransaction.py

@@ -73,9 +73,8 @@ class RawTransactionsTest(BitcoinTestFramework):
             ["-txindex"],
             ["-fastprune", "-prune=1"],
         ]
-        # whitelist all peers to speed up tx relay / mempool sync
-        for args in self.extra_args:
-            args.append("-whitelist=noban@127.0.0.1")
+        # whitelist peers to speed up tx relay / mempool sync
+        self.noban_tx_relay = True
         self.supports_cli = False
 
     def setup_network(self):