Merge bitcoin/bitcoin#25353: Add a -mempoolfullrbf node setting

4c9666bd73 Mention `mempoolfullrbf` in policy/mempool-replacements.md (Antoine Riard)
aae66ab43d Update getmempoolinfo RPC with `mempoolfullrbf` (Antoine Riard)
3e27e31727 Introduce `mempoolfullrbf` node setting. (Antoine Riard)

Pull request description:

  This is ready for review.

  Recent discussions among LN devs have brought back on the surface concerns about the security of multi-party funded transactions against pinnings attacks and other mempool-based nuisances. The lack of full-rbf transaction-relay topology connected to miners open the way to cheap and naive DoS against multi-party funded transactions (e.g coinjoins, dual-funded channels, on-chain DLCs, ...) without solutions introducing an overhead cost or centralization vectors afaik . For more details, see [0].

  This PR implements a simple `fullrbf` setting, where the node always allows transaction replacement, ignoring BIP125 opt-in flag. The default value of the setting stays **false**, therefore opt-in replacement is still the default Bitcoin Core replacement policy. Contrary to a previous proposal of mine and listening to feedbacks collected since then [1], I think this new setting simply offers more flexibility in a node transaction-relay policy suiting one's application requirements, without arguing a change of the default behavior.

  I [posted](https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-June/020557.html) on the ML to invite operators with a bitcoin application sensitive to full-rbf (e.g dual-funded LN channels service providers) or mempool researchers to join a bootstrapped full-rbf activated peers network for experimentation and learning. If people have strong opinions against the existence of such full-rbf transaction-relay network, I'm proposing to express them on the future thread.

  [0] https://lists.linuxfoundation.org/pipermail/lightning-dev/2021-May/003033.html
  [1] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-June/019074.html

  Follow-up suggestions :
  - soft-enable opt-in RBF in the wallet : https://github.com/bitcoin/bitcoin/pull/25353#issuecomment-1154918789
  - p2p discovery and additional outbound connection to full-rbf peers : https://github.com/bitcoin/bitcoin/pull/25353#issuecomment-1156044401
  - match the code between RPC, wallet and mempool about disregard of inherited signaling : #22698

ACKs for top commit:
  instagibbs:
    reACK 4c9666bd73
  glozow:
    ACK 4c9666bd73, a few nits which are non-blocking.
  w0xlt:
    ACK 4c9666bd73

Tree-SHA512: 9e288bf22e06a9808804e58178444ef1830c3fdd42fd8a7cd7ffb101f8f586e08b000679be407d63ca76a56f7216227b368ff630c81f3fac3243db1a1202ab1c

test/functional/feature_rbf.py

@@ -83,6 +83,9 @@ class ReplaceByFeeTest(BitcoinTestFramework):
         self.log.info("Running test replacement relay fee...")
         self.test_replacement_relay_fee()
 
+        self.log.info("Running test full replace by fee...")
+        self.test_fullrbf()
+
         self.log.info("Passed")
 
     def make_utxo(self, node, amount, *, confirmed=True, scriptPubKey=None):
@@ -698,5 +701,33 @@ class ReplaceByFeeTest(BitcoinTestFramework):
         tx.vout[0].nValue -= 1
         assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx.serialize().hex())
 
+    def test_fullrbf(self):
+        txid = self.wallet.send_self_transfer(from_node=self.nodes[0])['txid']
+        self.generate(self.nodes[0], 1)
+        confirmed_utxo = self.wallet.get_utxo(txid=txid)
+
+        self.restart_node(0, extra_args=["-mempoolfullrbf=1"])
+
+        # Create an explicitly opt-out transaction
+        optout_tx = self.wallet.send_self_transfer(
+            from_node=self.nodes[0],
+            utxo_to_spend=confirmed_utxo,
+            sequence=SEQUENCE_FINAL,
+            fee_rate=Decimal('0.01'),
+        )
+        assert_equal(False, self.nodes[0].getmempoolentry(optout_tx['txid'])['bip125-replaceable'])
+
+        conflicting_tx = self.wallet.create_self_transfer(
+                utxo_to_spend=confirmed_utxo,
+                sequence=SEQUENCE_FINAL,
+                fee_rate=Decimal('0.02'),
+        )
+
+        # Send the replacement transaction, conflicting with the optout_tx.
+        self.nodes[0].sendrawtransaction(conflicting_tx['hex'], 0)
+
+        # Optout_tx is not anymore in the mempool.
+        assert optout_tx['txid'] not in self.nodes[0].getrawmempool()
+
 if __name__ == '__main__':
     ReplaceByFeeTest().main()