net: tun: remove useless codes of tun_automq_select_queue

Because the function __skb_get_hash_symmetric always returns non-zero.

Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Wang Li <wangli39@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>