lnwallet: fix ordering of keys when we generate the sender script during a breach

In this commit, we fix an existing within lnd. Before this commit,
within NewBreachRetribution the order of the keys when generating the
sender HTLC script was incorrect. As in this case, the remote party is
the sender, their key should be first. However, the order was swapped,
meaning that at breach time, our transaction would be rejected as it had
the incorrect witness script.

The fix is simple: swap the ordering of the keys. After this commit, the
test extension added in the prior commit now passes.

lnwallet/channel.go

@@ -1992,7 +1992,7 @@ func NewBreachRetribution(chanState *channeldb.OpenChannel, stateNum uint64,
 		// re-generate the sender HTLC script.
 		if htlc.Incoming {
 			htlcScript, err = senderHTLCScript(
-				keyRing.LocalHtlcKey, keyRing.RemoteHtlcKey,
+				keyRing.RemoteHtlcKey, keyRing.LocalHtlcKey,
 				keyRing.RevocationKey, htlc.RHash[:],
 			)
 			if err != nil {