[NET] fs/proc/proc_net.c: make a struct static

Struct proc_net_ns_ops can become static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>