net: hns3: get FD rules location before dump in debugfs

Currently, the dump FD tcam mode in debugfs is to query all FD tcams,
including empty rules, which is unnecessary. This patch modify to
find the position of useful rules before dump FD tcam, so that it does
not need to query empty rules.

This patch also modifies some help information in debugfs.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>