s3-smbd: move print_backend_init() behind init_system_info()

s3-smbd: move print_backend_init() behind init_system_info()

On smbd startup check_published_printers() fails with the following error
messages:

[2012/04/04 16:29:50.511526,  0] printing/nt_printing_ads.c:360(check_published_printers)
  check_published_printers: Could not create system session_info
[2012/04/04 16:29:50.512101,  0] printing/nt_printing.c:102(nt_printing_init)
  nt_printing_init: error checking published printers: WERR_ACCESS_DENIED

check_published_printers() requires session_info to be set, but
initialization of session_info in main() is done after calling
print_backend_init(). Move print_backend_init() behind init_system_info().

Signed-off-by: Ralph Wuerthner <ralph.wuerthner@de.ibm.com>
Fix bug #8845 (check_published_printers: Could not create system session_info).