net: hns3: refactor GL update function

The GL update function uses the max GL value between tx_int_gl and
rx_int_gl to set both new tx_int_gl and new rx_int_gl. Therefore, User
can not enable TX GL self-adaptive or RX GL self-adaptive individually.

This patch refactors the code to update the TX GL and the RX GL
separately, making user can enable TX GL self-adaptive or RX GL
self-adaptive individually.

Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>