collectd: move jshn.sh include to remove warning

Redmine-patch-id: 3680
If I build an image with the imagebuilder I get the following output
during image building:

../root-x86/etc/init.d/collectd: line 4: /usr/share/libubox/jshn.sh:
No such file or directory

To remove this messsage move include to the needed postion, so that the
message does not occur during image building on the host system anymore.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
(cherry-picked, modified to match 19.07)
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>