Fix psample build error when CONFIG_INET is not set/enabled by
bracketing the tunnel code in #ifdef CONFIG_NET / #endif.

../net/psample/psample.c: In function ‘__psample_ip_tun_to_nlattr’:
../net/psample/psample.c:216:25: error: implicit declaration of function ‘ip_tunnel_info_opts’; did you mean ‘ip_tunnel_info_opts_set’? [-Werror=implicit-function-declaration]
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Yotam Gigi <yotam.gi@gmail.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>