Check bmx7 was installed

src/freedombone-mesh-batman

@@ -60,7 +60,9 @@ function stop {
     fi
 
     systemctl stop bmx6
-    systemctl stop bmx7
+    if [ -d /etc/bmx7 ]; then
+        systemctl stop bmx7
+    fi
     systemctl stop olsr2
     systemctl stop babel
     systemctl disable bmx6