[reboot cause]: Delay process-reboot-cause service until network connection is stable (sonic-net#4003)

Author: sujinmkang

files/build_templates/process-reboot-cause.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Delays process-reboot-cause until network is stably connected
+
+[Timer]
+OnBootSec=1min 30 sec
+Unit=process-reboot-cause.service
+
+[Install]
+WantedBy=timers.target

files/build_templates/sonic_debian_extension.j2

@@ -283,6 +283,11 @@ sudo cp $IMAGE_CONFIGS/procdockerstatsd/procdockerstatsd.service  $FILESYSTEM_RO
 echo "procdockerstatsd.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/procdockerstatsd/procdockerstatsd $FILESYSTEM_ROOT/usr/bin/
 
+# Copy systemd timer configuration
+# It implements delayed start of services
+sudo cp $BUILD_TEMPLATES/process-reboot-cause.timer $FILESYSTEM_ROOT/etc/systemd/system/
+sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable process-reboot-cause.timer
+
 # Copy process-reboot-cause service files
 sudo cp $IMAGE_CONFIGS/process-reboot-cause/process-reboot-cause.service  $FILESYSTEM_ROOT/etc/systemd/system/
 echo "process-reboot-cause.service" | sudo tee -a $GENERATED_SERVICE_FILE

files/image_config/process-reboot-cause/process-reboot-cause.service

@@ -5,6 +5,3 @@ After=rc-local.service
 [Service]
 Type=simple
 ExecStart=/usr/bin/process-reboot-cause
-
-[Install]
-WantedBy=multi-user.target