Change NotifyAccess from "main" to "all"

sd_notify() is called from other threads (PIDs), so we've been getting
syslog warnings abouts this and I hadn't noticed:

systemd[1]: sbbs.service: Got notification message from PID 2555007, but reception only permitted for main PID which is currently not known

As pointed out by Accession (PHARCYDE) on DOVE-Net.

install/systemd/sbbs.service

@@ -22,7 +22,7 @@ After=syslog.target network-online.target
 
 [Service]
 Type=forking
-NotifyAccess=main
+NotifyAccess=all
 Environment=SBBSCTRL=/sbbs/ctrl
 User=sbbs
 Group=sbbs