Follow-up from "allow dns_clientinfo to store client ECS data"

The following discussion from !5555 (merged) should be addressed:

• @ondrej started a discussion: (+1 comment)

  Honestly, I would not change dns_clientinfo_init(), but would rather add extra function to set the ecs in the structure:

  void
  dns_clientinfo_init(dns_clientinfo_t *ci, void *data, void *versionp);
  
  void
  dns_clientinfo_set_ecs(dns_clientinfo_t *ci, dns_ecs_t *ecs);

  That way the amount of changes to the other code would be minimized as if I count correctly, it's only three places, where we set the ecs data in the dns_clientinfo structure.