net: hns3: getting tx and dv buffer size through firmware

This patch adds support of getting tx and dv buffer size through
firmware, because different version of hardware requires different
size of tx and dv buffer.

This patch also add dv_buf_size to tc' private buffer size even if
pfc is not enable for the tc.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>