dns: sort the ip-data list when a new element is added
In nm_dns_manager_set_ip_config() we try to avoid calling update_dns()
unless something changes, because updating DNS is expensive and can
trigger other actions such as a new hostname resolution.
When we add a new ip_data, even if the new element is equivalent to the old one that was removed, we need to sort the list again.
Fixes: ce0a36d2 ('dns: better track l3cd changes')