bundles/pppd: make sure dependent services are stopped before restarting pppoe session

bundles/pppd/files/wait-until-stopped

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+% for service in sorted(services):
+(
+    while true
+    do
+        if systemctl is-active ${service}
+        then
+            sleep 1
+        else
+            exit 0
+        fi
+    done
+) &
+% endfor
+
+wait