Enforce limitless TNs after limit removal in TNR

We want the limit removal to be completely done once we do it. When new
TN are deployed afterwards, they must be deployed without limits.

Closes #1416

raiden_contracts/data/source/raiden/TokenNetworkRegistry.sol

@@ -75,6 +75,13 @@ contract TokenNetworkRegistry is Utils {
         canCreateTokenNetwork
         returns (address token_network_address)
     {
+        // After the limits have been removed, new token networks must be created without limits
+        // See https://github.com/raiden-network/raiden-contracts/issues/1416
+        if (max_token_networks == MAX_INT) {
+            require(_channel_participant_deposit_limit == MAX_INT, "Limits must be set to MAX_INT");
+            require(_token_network_deposit_limit == MAX_INT, "Limits must be set to MAX_INT");
+        }
+
         require(token_to_token_networks[_token_address] == address(0x0));
 
         // We limit the number of token networks to 1 for the Bug Bounty release

raiden_contracts/tests/test_contract_limits.py

@@ -14,7 +14,7 @@
     ParticipantInfoIndex,
 )
 from raiden_contracts.tests.utils import call_and_transact
-from raiden_contracts.tests.utils.constants import DEPLOYER_ADDRESS
+from raiden_contracts.tests.utils.constants import DEPLOYER_ADDRESS, UINT256_MAX
 
 
 def test_register_three_but_not_four(
@@ -69,11 +69,19 @@ def test_register_three_but_not_four(
 
     # Now remove the limit and try again
     call_and_transact(token_network_registry.functions.removeLimits(), {"from": DEPLOYER_ADDRESS})
+    with pytest.raises(TransactionFailed, match="Limits must be set to MAX_INT"):
+        call_and_transact(
+            token_network_registry.functions.createERC20TokenNetwork(
+                token4.address,
+                channel_participant_deposit_limit,
+                token_network_deposit_limit,
+            )
+        )
     call_and_transact(
         token_network_registry.functions.createERC20TokenNetwork(
             token4.address,
-            channel_participant_deposit_limit,
-            token_network_deposit_limit,
+            UINT256_MAX,
+            UINT256_MAX,
         )
     )