Merge #19423: test: add functional test for txrelay during and after IBD

cb31ee01b4 [test] feefilter during and after IBD (gzhao408)

Pull request description:

  This is a followup to #19204 which uses `minfeefilter=MAX_MONEY` to effectively shut off txrelay, thereby reducing inv traffic, when nodes are in IBD. It was [missing](https://github.com/bitcoin/bitcoin/pull/19204#issuecomment-644040070) a functional test.

ACKs for top commit:
  jnewbery:
    utACK cb31ee01b4

Tree-SHA512: a9effc8193fa95fb42a2f9c66b258cc7b0941fc04c1ce3a6092f4426c9bfc7e72f702aca559b3e30e90652497f411f22fae3cf5cdb6cfd6ef6d37fed712cda67

test/functional/test_runner.py

@@ -248,6 +248,7 @@ BASE_SCRIPTS = [
     'rpc_help.py',
     'feature_help.py',
     'feature_shutdown.py',
+    'p2p_ibd_txrelay.py',
     # Don't append tests at the end to avoid merge conflicts
     # Put them in a random line within the section that fits their approximate run-time
 ]