gluon-core: migrate lan role of single port config

when a device is migrated from a single WAN/LAN configuration to a
multi-port configuration (e.g. using DSA), set the same role on all
ports and not just the new WAN port.

package/gluon-core/luasrc/lib/gluon/upgrade/021-interface-roles

@@ -43,6 +43,7 @@ if uci:get('gluon', 'iface_wan') then
 end
 if uci:get('gluon', 'iface_single') then
 	roles.wan = uci:get_list('gluon', 'iface_single', 'role')
+	roles.lan = uci:get_list('gluon', 'iface_single', 'role')
 end
 
 -- Non-existing interfaces are nil, so they will not be added to the table