batman_adv: Dont remove not existing dkms module

batman_adv/kmod.sls

@@ -58,6 +58,7 @@ batman-adv_dkms_install:
 batman-adv_dkms_remove:
   cmd.run:
     - name: dkms remove batman_adv --all
+    - onlyif: which dkms && dkms status | grep batman_adv
 
 {%- endif %}