fix(systemd): unit file was missing the requires directive (#32)

This could cause the mgmtd to startup with only the loopback device advertised to other services.

This also switches to use network-online.target instead of network.target, consistent with the BeeGFS 7 mgmtd.

Author: iamjoemccormick

mgmtd/assets/beegfs-mgmtd.service

@@ -1,7 +1,8 @@
 [Unit]
 Description=BeeGFS Management Server
 Documentation=https://doc.beegfs.io
-After=network.target
+Requires=network-online.target 
+After=network-online.target
 
 [Service]
 Type=notify