[tests] Test that nodes respond to getdata with notfound

If a node has not announced a tx at all, then it should respond to
getdata messages for that tx with notfound, to avoid leaking tx
origination privacy.

test/functional/test_runner.py

@@ -152,6 +152,7 @@ BASE_SCRIPTS = [
     'feature_versionbits_warning.py',
     'rpc_preciousblock.py',
     'wallet_importprunedfunds.py',
+    'p2p_leak_tx.py',
     'rpc_signmessage.py',
     'feature_nulldummy.py',
     'mempool_accept.py',