net: hns3: give default option while dependency HNS3 set

Give default option for HNS3_HCLGE and HNS3_ENET will be helpful,
while dependency HNS3 is set. Meanwhile, use "if HNS3" section
instead of all the "depends on HNS3".

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>