session_track_trx_state set to true causes incorrect routing of SELECT

Any of the following conditions inside a transaction can cause the following SELECT to return the incorrect value:

Client connects to maxscale, which is configured with session_track_trx_state = TRUE
Client issues `set autocommit=0;`
Client performs an insert via an `INSERT... RETURNING` statement

The failing action is the next one, namely:

Client performs a SELECT operation immediately after the `INSERT... RETURNING` statement which involves data from the previously inserted row