webadmin: fix feedback link popup scrollbars

- Add scrollbars to feedback link popup call, so it
  doesn't open in window that cannot be manipulated.

Change-Id: Ib7d6166298409485e1c7eb3bc12ecf79397b5e69
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1107799
Signed-off-by: Alexander Wels <awels@redhat.com>