systemd.bbclass: restart service in postinst, not start
When upgrading packages it's possible that the service is already running
because opkg doesn't actually execute the prerm hooks on upgrades, which is
where the service should be stopped.
Handle this case by restarting in postinst instead of starting. If the service
isn't already running then this doesn't make a difference, but if it is running
then the service will be restarted.
[ YOCTO #4213 ]
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
