Fix #4038: Attempting to create an IP-ban bans the creator.

* Rename comments.ip_addr to comments.creator_ip_addr.
* Fix belongs_to_creator to not clobber ip_addr field.

db/migrate/20190109210822_rename_ip_addr_on_comments.rb

@@ -0,0 +1,5 @@
+class RenameIpAddrOnComments < ActiveRecord::Migration[5.2]
+  def change
+    rename_column :comments, :ip_addr, :creator_ip_addr
+  end
+end