Set working directory in systemd service file

By default systemd will execute service with root directory (or home directory for user instance) which might result in
attempts to create files in unexpected place. Let's set it to 'osmocom' subdir of state directory (/var/lib for system instance) instead.

Fixes: OS#5661
Change-Id: I0f942545d9e920ba8a2d8645512ec3414ab27418
diff --git a/contrib/systemd/osmo-msc.service b/contrib/systemd/osmo-msc.service
index 343639c..36849f7 100644
--- a/contrib/systemd/osmo-msc.service
+++ b/contrib/systemd/osmo-msc.service
@@ -8,6 +8,8 @@
 [Service]
 Type=simple
 Restart=always
+StateDirectory=osmocom
+WorkingDirectory=%S/osmocom
 ExecStart=/usr/bin/osmo-msc -c /etc/osmocom/osmo-msc.cfg
 RestartSec=2