dmails: set sender name and ip address explicitly.

Set the sender name and IP addresses explicitly in the controller rather
than implicitly in the model.

Fixes cases where automated dmails from DanbooruBot had their IP
addresses set to the person who triggered the dmail, even though they
didn't actually send the dmail themselves.

app/controllers/dmails_controller.rb

@@ -33,7 +33,7 @@ class DmailsController < ApplicationController
   end
 
   def create
-    @dmail = Dmail.create_split(dmail_params(:create))
+    @dmail = Dmail.create_split(from: CurrentUser.user, creator_ip_addr: CurrentUser.ip_addr, **dmail_params(:create))
     respond_with(@dmail)
   end