rpc: recognize the new unused prefix address types

mock.go

@@ -226,6 +226,11 @@ func (m *mockWalletController) NewAddress(addrType lnwallet.AddressType,
 		m.rootKey.PubKey().SerializeCompressed(), &chaincfg.MainNetParams)
 	return addr, nil
 }
+func (*mockWalletController) LastUnusedAddress(addrType lnwallet.AddressType) (
+	btcutil.Address, error) {
+	return nil, nil
+}
+
 func (*mockWalletController) IsOurAddress(a btcutil.Address) bool {
 	return false
 }