net: hns3: reallocate SSU' buffer size when pfc_en changes

When a TC's PFC is disabled or enabled, the RX private buffer for
this TC need to be changed too, otherwise this may cause packet
dropped problem.

This patch fixes it by calling hclge_buffer_alloc to reallocate
buffer when pfc_en changes.

Fixes: cacde272

 ("net: hns3: Add hclge_dcb module for the support of DCB feature")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>