Possible breakage in SystemMulticastRoutingGenerator
At the end of `SystemMulticastRoutingGenerator._add_routing_entries` we see this:

https://github.com/SpiNNakerManchester/SpiNNFrontEndCommon/blob/f5f1741a111b804a921af59b0537c1a471dc5787/spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py#L180

That line is weird because it appears to be doing an increment that cannot have any effect. Should it be indented one level further so that it goes inside the loop immediately above it? That'd make sort of sense from a general-algorithmic-pattern sense.
diff --git a/spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py b/spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py
index fa249ad2b..ea6fd7c87 100644
--- a/spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py
+++ b/spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py
@@ -221,4 +221,3 @@ class SystemMulticastRoutingGenerator(object):
                 link_ids=links_per_chip[x, y])
             # update tracker
             self._time_out_keys_by_board[(eth_x, eth_y)] = key
-        key += N_KEYS_PER_REINJECTION_PARTITION
['spinn_front_end_common/interface/interface_functions/system_multicast_routing_generator.py']