Problem is that altough the defconfig says the tun driver should be made available as a module, it isn't (in 7.0-release):
[root@openpli-dist lunix]# ls -l | grep kernel-module-tu -rwxrwsr--. 1 root openpli 3622 Jan 11 20:28 kernel-module-tua9001-4.2.1_4.2.1-r0.1_lunix.ipk -rwxrwsr--. 1 root openpli 11856 Jan 11 20:28 kernel-module-tuner-4.2.1_4.2.1-r0.1_lunix.ipk -rwxrwsr--. 1 root openpli 3478 Jan 11 20:28 kernel-module-tunnel4-4.2.1_4.2.1-r0.1_lunix.ipk -rwxrwsr--. 1 root openpli 3500 Jan 11 20:28 kernel-module-tunnel6-4.2.1_4.2.1-r0.1_lunix.ipk
7.1-rc has the same issue.
Due to personal circumstances I can't look at it for the next two weeks. Please ping me again first week of June, in case I forget this...