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/wallet_send.py

@@ -30,10 +30,11 @@ class WalletSendTest(BitcoinTestFramework):
 
     def set_test_params(self):
         self.num_nodes = 2
-        # whitelist all peers to speed up tx relay / mempool sync
+        # whitelist peers to speed up tx relay / mempool sync
+        self.noban_tx_relay = True
         self.extra_args = [
-            ["-whitelist=127.0.0.1","-walletrbf=1"],
-            ["-whitelist=127.0.0.1","-walletrbf=1"],
+            ["-walletrbf=1"],
+            ["-walletrbf=1"]
         ]
         getcontext().prec = 8 # Satoshi precision for Decimal