encode_page_control() must have a 2nd argument T5734

Summary:
As reported in T5734 kolab sync and kolabd are crashing
with a trackback that encode_page_control must have 2 arguments. Adding
the empty cookie attribute to the server_page_controls removed the error.

Reviewers: PyKolab Developers, vanmeeuwen

Reviewed By: PyKolab Developers, vanmeeuwen

Differential Revision: https://git.kolab.org/D895