test: speed up wallet_avoidreuse.py

Use -whitelist to speed up transaction relay.

The wallet_avoidreuse.py test is not intended to test transaction relay/timing,
so it should be fine to do this here.

This greatly reduces test run time variability and speeds up the test by 2-3
times on average, e.g. on my system from 20-30 seconds down to 8-10 seconds.

test/functional/wallet_avoidreuse.py

@@ -67,6 +67,9 @@ class AvoidReuseTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = False
         self.num_nodes = 2
+        # This test isn't testing txn relay/timing, so set whitelist on the
+        # peers for instant txn relay. This speeds up the test run time 2-3x.
+        self.extra_args = [["-whitelist=127.0.0.1"]] * 2
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()