Please reinstate remote access to maxscaled protocol

Starting with 2.0.0, remote access to maxscaled protocol (maxadmin listener) has been removed in favor of domain sockets only.

This change impacts external applications such as replication-manager, that could potentially talk remotely with MaxScale.

I suggest reinstating the remote protocol, but make it admin-only. The default settings for maxscale should always go to domain sockets, and the default user (admin/mariadb) shouldn't have privileges to connect remotely. In order to connect the operator would have to create a different user with specific remote privileges.