so when allowing both a port and socket like:

[Splitter Listener]
type=listener
service=Splitter Service
protocol=MySQLClient
port=3306
socket=/tmp/ClusterMaster

it returns the error:

2017-09-12 15:43:51 error : Listener 'Splitter-Listener', for service 'Splitter-Service', already have port 3306.
2017-09-12 15:43:51 error : 1 errors were encountered while processing the configuration file '/etc/maxscale.cnf'.
2017-09-12 15:43:51 error : Failed to open, read or process the MaxScale configuration file /etc/maxscale.cnf. Exiting.

saying there already is a port 3306 is incorrect, but it should allow both socket as port bindings in the same listener. It seems conflicting.

In the 2.0.1. ubuntu release it was possible to open both port and socket in the same listener.