SET DEFAULT ROLE is not classified as a write

The SET DEFAULT ROLE command modifies the database by changing the defaut role the user uses. This is a replicated command and is currently classified as a session command. As a result of this, the modification is done on all servers when it should only be done on the current master.

Original description:

maxscale r/w readwritesplit send SET DEFAULT ROLE to all nodes and write on slaves as well