Merge #15330: test: Fix race in p2p_invalid_messages

fac3a054cb test: Fix race in p2p_invalid_messages (MarcoFalke)

Pull request description:

  After we change our magic bytes, the node may or may not send us messages such as feefilter or sendheaders, which would be rejected by `_on_data`.

  Solve that by replacing `_on_data` with a noop.

Tree-SHA512: bd25a81f0c6e31f09155e00abab8062777d827b9210d6a9b85ef35cfe5069338f100fecf058842f41a1f134fdb3cf7ac1fe80db493e4dab7988acdacb33149df

test/functional/p2p_invalid_messages.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright (c) 2015-2018 The Bitcoin Core developers
+# Copyright (c) 2015-2019 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test node responses to invalid network messages."""
@@ -143,6 +143,7 @@ class InvalidMessagesTest(BitcoinTestFramework):
 
     def test_magic_bytes(self):
         conn = self.nodes[0].add_p2p_connection(P2PDataStore())
+        conn._on_data = lambda: None  # Need to ignore all incoming messages from now, since they come with "invalid" magic bytes
         conn.magic_bytes = b'\x00\x11\x22\x32'
         with self.nodes[0].assert_debug_log(['PROCESSMESSAGE: INVALID MESSAGESTART ping']):
             conn.send_message(messages.msg_ping(nonce=0xff))
@@ -211,6 +212,5 @@ class InvalidMessagesTest(BitcoinTestFramework):
         return raw_msg_with_wrong_size
 
 
-
 if __name__ == '__main__':
     InvalidMessagesTest().main()