wallet: (fix) "batch_rbf" must not mutate LN funding txs

The "Batch RBF transactions" feature mutates existing "local" and "unconfirmed RBF"
transactions when creating new transactions: it simply adds the new outputs to the
existing txs (and updates the change).
The "RBF" flag is only enforced for unconfirmed txs, not for local txs.
The bug was that given a local LN funding tx, when creating a new channel
with "batch_rbf" enabled, we would modify the existing local tx, and
broadcast that.

related: #7298

electrum/wallet.py

@@ -586,6 +586,10 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         """Returns a map: pubkey -> (keystore, derivation_suffix)"""
         return {}
 
+    def is_lightning_funding_tx(self, txid: str) -> bool:
+        return any([chan.funding_outpoint.txid == txid
+                    for chan in self.lnworker.channels.values()])
+
     def get_tx_info(self, tx: Transaction) -> TxWalletDetails:
         tx_wallet_delta = self.get_wallet_delta(tx)
         is_relevant = tx_wallet_delta.is_relevant
@@ -598,8 +602,7 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         tx_hash = tx.txid()  # note: txid can be None! e.g. when called from GUI tx dialog
         is_lightning_funding_tx = False
         if self.has_lightning() and tx_hash is not None:
-            is_lightning_funding_tx = any([chan.funding_outpoint.txid == tx_hash
+            is_lightning_funding_tx = self.is_lightning_funding_tx(tx_hash)
-                                           for chan in self.lnworker.channels.values()])
         tx_we_already_have_in_db = self.db.get_transaction(tx_hash)
         can_save_as_local = (is_relevant and tx.txid() is not None
                              and (tx_we_already_have_in_db is None or not tx_we_already_have_in_db.is_complete()))
@@ -1241,6 +1244,9 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
             # all inputs should be is_mine
             if not all([self.is_mine(self.get_txin_address(txin)) for txin in tx.inputs()]):
                 continue
+            # do not mutate LN funding txs, as that would change their txid
+            if self.is_lightning_funding_tx(txid):
+                continue
             # prefer txns already in mempool (vs local)
             if hist_item.tx_mined_status.height == TX_HEIGHT_LOCAL:
                 candidate = tx