net: sched: act_tunnel_key: get rid of tunnel_key_walker and tunnel_key_search

tunnel_key_walker() and tunnel_key_search() do the same thing as generic
walk/search function, so remove them.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>