net: hns3: check for NULL function pointer in hns3_nic_set_features

It's necessary to check hook whether being defined before
calling, improve the reliability.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>