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/feature_csv_activation.py

@@ -95,8 +95,9 @@ class BIP68_112_113Test(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 1
         self.setup_clean_chain = True
+        # whitelist peers to speed up tx relay / mempool sync
+        self.noban_tx_relay = True
         self.extra_args = [[
-            '-whitelist=noban@127.0.0.1',
             f'-testactivationheight=csv@{CSV_ACTIVATION_HEIGHT}',
             '-par=1',  # Use only one script thread to get the exact reject reason for testing
         ]]