When determining which servers to monitor, =remove special handling of setVersion reported by ismaster that was added in 2.12.0. It's more reliable to instead to rely on whatever is reported by the primary, if the driver can connect to it.

The driver should only start monitoring new servers if they are reported by the primary or if it isn't connected to the primary. The driver should only stop monitoring servers if the primary reports that they are no longer part of the replica set.