docs: fix literal blocks

docs/features/mesh-on-wan.rst

@@ -1,15 +1,13 @@
 Mesh on WAN
 ===========
 
-It's possible to enable the mesh on the WAN port like this:
+It's possible to enable the mesh on the WAN port like this::
 
-  ::
   uci set network.mesh_wan.auto=1
   uci commit
 
-It may also be disabled again by running:
+It may also be disabled again by running::
 
-  ::
   uci set network.mesh_wan.auto=0
   uci commit