Name unk field in email

Co-Authored-By: ratkosrb <35845488+ratkosrb@users.noreply.github.com>

Author: killerwife

src/game/Mails/MailHandler.cpp

@@ -586,7 +586,7 @@ void WorldSession::HandleGetMailList(WorldPacket& recv_data)
 
         data << (*itr)->subject;                            // Subject string - once 00, when mail type = 3
         data << uint32((*itr)->itemTextId);                 // sure about this
-        data << uint32(0);                                  // unknown
+        data << uint32(0);                                  // package (Package.dbc)
         data << uint32((*itr)->stationery);                 // stationery (Stationery.dbc)
 
         // 1.12.1 can have only single item