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_cltv.py

@@ -83,9 +83,10 @@ CLTV_HEIGHT = 111
 class BIP65Test(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 1
+        # whitelist peers to speed up tx relay / mempool sync
+        self.noban_tx_relay = True
         self.extra_args = [[
             f'-testactivationheight=cltv@{CLTV_HEIGHT}',
-            '-whitelist=noban@127.0.0.1',
             '-par=1',  # Use only one script thread to get the exact reject reason for testing
             '-acceptnonstdtxn=1',  # cltv_invalidate is nonstandard
         ]]