net: make struct tun_struct private to tun.c

There's no reason for this to be in the header, and it just hurts
recompile time.

Signed-off-by: Rusty Russell <[email protected]>
Acked-by: Max Krasnyanskiy <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
3 files changed