tun: use tun_sk instead container_of
tun: use tun_sk instead container_of

Using macro tun_sk is more clear and shorter. However tun.c has tun_sk,
but doesn't use it.

Signed-off-by: Vitaliy Gusev <c947270679a5086de9925da9e526c9b7b510120c@openvz.org>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas