net: hns3: add option to turn off page pool feature

When page pool is added to the hns3 driver, it is always
enabled unconditionally, which means spilt page handling
in the hns3 driver is dead code.

As there is a requirement to test the performance between
spilt page handling in driver and page pool, so add a module
param to support disabling the page pool.

When the page pool is proved to perform better in most case,
the spilt page handling in driver can be removed.

Fixes: 93188e96

 ("net: hns3: support skb's frag page recycling based on page pool")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>