net: hns: bug fix about hisilicon TSO BD mode

The current upstreaming code fails to set the tso_mode register
when initilizes, when processes large size packets, the default 4 bd is
not enough, so this patch initilizes it and set the default value to 8 bds

Signed-off-by: Daode Huang <huangdaode@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>