Bug 25992: Make SIP2 logger subroutines exportable to prevent crash

Bug 25992: Make SIP2 logger subroutines exportable to prevent crash

If the subroutines are not exportable we get the following crash:

> Undefined subroutine &C4::SIP::SIPServer::set_logger

To test:
 In kohadevbox run for example:
 $ ps -aux # check that no existing sip server is running, kill the process if exists
 $ perl /kohadevbox/koha/C4/SIP/SIPServer.pm /etc/koha/sites/kohadev/SIPconfig.xml
 $ koha/misc/sip_cli_emulator.pl -su koha -sp koha -l CPL -a 127.0.0.1 -p 6001 --item 3999900000001 -m item_information

 After applying this patch the Undefined subroutine error should be gone.
 Note: when using the sip_cli_emulator.pl the credentials can be anything.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>