Dynamic filter capabilities do not work

The dynamic filter capability calculation does not work. The capabilities are read before filter is configured.

The nullfilter is the only one that actually defines a dynamic set of capabilites so the practical effects are quite minimal. However, as MXS-4549 demonstrates, there is a real-world need which the nullfilter could be used to fix: by using a nullfilter with capabilities=RCAP_TYPE_RESULTSET_OUTPUT in a readwritesplit service, a deadlocked stored procedure call would end up being successfully replayed. This happens because the filter requests that the complete result is collected before being delivered to the filter. This has the side-effect of preventing partial results from being delivered to the client.