luci-base: network.lua: fix interface.ports() function return value

Signed-off-by: Anton Kikin <a.kikin@tano-systems.com>

modules/luci-compat/luasrc/model/network.lua

@@ -1447,6 +1447,7 @@ function interface.ports(self)
 		for _, iface in ipairs(members) do
 			ifaces[#ifaces+1] = interface(iface)
 		end
+		return ifaces
 	end
 end