test: add functional test for private broadcast

test/functional/test_runner.py

@@ -300,6 +300,7 @@ BASE_SCRIPTS = [
     'rpc_dumptxoutset.py',
     'feature_minchainwork.py',
     'rpc_estimatefee.py',
+    'p2p_private_broadcast.py',
     'rpc_getblockstats.py',
     'feature_port.py',
     'feature_bind_port_externalip.py',