channeldb+lnwallet: store updates the peer should sign under new key

This fixes a long-standing force close bug. When we receive a
revocation, store the updates that the remote should sign next under
a new database key. Previously, these were not persisted which would
lead to force closure.

channeldb/db_test.go

@@ -398,7 +398,7 @@ func TestRestoreChannelShells(t *testing.T) {
 	if err != ErrNoRestoredChannelMutation {
 		t.Fatalf("able to mutate restored channel")
 	}
-	err = channel.AdvanceCommitChainTail(nil)
+	err = channel.AdvanceCommitChainTail(nil, nil)
 	if err != ErrNoRestoredChannelMutation {
 		t.Fatalf("able to mutate restored channel")
 	}