reverse swaps: in the CLI, replace 'server_mining_fee' with

'prepayment', which corresponds to the trusted part of the
lightning payment.

We use 2*sm.mining_fee, where 'mining_fee' is the flat part of
the server fee. However, future protocol should probably allow
to set a value that does not depend on 'mining_fee'.
(note that LND uses a hardcoded amount).

electrum/gui/qml/qeswaphelper.py

@@ -719,7 +719,7 @@ class QESwapHelper(AuthMixin, QObject, QtEventListener):
                     transport=self.swap_transport,
                     lightning_amount_sat=lightning_amount,
                     expected_onchain_amount_sat=onchain_amount + swap_manager.get_fee_for_txbatcher(),
-                    server_mining_fee_sat=self.serverMiningfee.satsInt,
+                    prepayment_sat=2 * self.serverMiningfee.satsInt,
                 )
                 try:  # swaphelper might be destroyed at this point
                     if txid:

electrum/gui/qt/swap_dialog.py

@@ -338,7 +338,7 @@ class SwapDialog(WindowModalDialog, QtEventListener):
                 transport=transport,
                 lightning_amount_sat=lightning_amount,
                 expected_onchain_amount_sat=onchain_amount + self.swap_manager.get_fee_for_txbatcher(),
-                server_mining_fee_sat=self.last_server_mining_fee_sat,
+                prepayment_sat=2 * self.last_server_mining_fee_sat,
             )
             try:
                 # we must not leave the context, so we use run_couroutine_dialog