fix deleting if and unless options from filters

I have next code in one of my AA applications which use dynamic filter using if, unless options
```
Report::CustomCdr::CDR_COLUMNS.each do |key|
      filter Report::CustomData.normalized_column_name(key.to_s).to_sym, :if => proc{
        @custom_cdr.group_by_include? key
      }
  end
```

It works , but only first time, after reloading page I all filters are on the sidebar like it was no :if . I started to debug and noticed that after first rendering, if and unless options are not used anymore, because they were deleted in active_admin_filters_form_for method.