net: hns3: Modify hns3_get_max_available_channels

The current hns3_get_max_available_channels returns the total number
of queues for the device, which makes ethtool -L set the number of queues
per channel queues incorrectly, so hns3_get_max_available_channels should
return the maximum available number of queues per channel, depending on
the total number of queues allocated and the hardware configurations.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>