Sort of aggregates by prefixes breaks RIR section

[avb1987]

NetBox version

v3.2.1

Python version

3.8

Steps to Reproduce

1. Go to "IPAM -> Aggregates", click on "Prefixes" column header in the aggregates table in order to sort aggregates by child prefix count.
2. Go to "IPAM -> RIRs", click on any RIR name to open its details.

Expected Behavior

RIR details should be displayed

Observed Behavior

Server error is displayed

`<class 'django.core.exceptions.FieldError'>

Cannot resolve keyword 'child_count' into field. Choices are: created, custom_field_data, date_added, description, id, journal_entries, last_updated, prefix, rir, rir_id, tagged_items, tags, tenant, tenant_id

Python version: 3.8.10
NetBox version: 3.2.1

`