Merge bitcoin/bitcoin#26396: net: Avoid SetTxRelay for feeler connections

fa24239a1c net: Avoid SetTxRelay for feeler connections (MacroFake)

Pull request description:

  Seems odd to reserve memory for the struct (the heaviest member being `m_tx_inventory_known_filter`) when it is never used.

  This also avoids sending out `msg_sendtxrcncl` before disconnecting. This shouldn't matter, as other messages, such as `msg_wtxidrelay`, `msg_sendaddrv2`, `msg_verack` or `msg_getaddr` are still sent. Though, it allows to test the changes here as a side-effect.

ACKs for top commit:
  naumenkogs:
    ACK fa24239a1c
  vasild:
    ACK fa24239a1c
  jonatack:
    ACK fa24239a1c
  mzumsande:
    ACK fa24239a1c

Tree-SHA512: d7604c7eb4df8f2de811e600bdd312440ee03e508d3a0f09ae79f7f2d3eeec663bfd47a2d079fa50b756d61e35dfa998de068a7b9afaf35378fa0e62a538263d

test/functional/p2p_sendtxrcncl.py

@@ -39,6 +39,12 @@ class SendTxrcnclReceiver(P2PInterface):
     def on_sendtxrcncl(self, message):
         self.sendtxrcncl_msg_received = message
 
+
+class P2PFeelerReceiver(SendTxrcnclReceiver):
+    def on_version(self, message):
+        pass  # feeler connections can not send any message other than their own version
+
+
 class PeerTrackMsgOrder(P2PInterface):
     def __init__(self):
         super().__init__()
@@ -163,6 +169,11 @@ class SendTxRcnclTest(BitcoinTestFramework):
         assert not peer.sendtxrcncl_msg_received
         peer.peer_disconnect()
 
+        self.log.info("SENDTXRCNCL should not be sent if feeler")
+        peer = self.nodes[0].add_outbound_p2p_connection(P2PFeelerReceiver(), p2p_idx=2, connection_type="feeler")
+        assert not peer.sendtxrcncl_msg_received
+        peer.peer_disconnect()
+
         self.log.info('SENDTXRCNCL if block-relay-only triggers a disconnect')
         peer = self.nodes[0].add_outbound_p2p_connection(
             PeerNoVerack(), wait_for_verack=False, p2p_idx=3, connection_type="block-relay-only")