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

spesmilo/electrum,wakiyamap/electrum-mona,spesmilo/electrum,pooler/electrum-ltc,pooler/electrum-ltc,pooler/electrum-ltc,spesmilo/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona,wakiyamap/electrum-mona,spesmilo/electrum,wakiyamap/electrum-mona