net: hns3: Add support for dynamically buffer reallocation

Current buffer allocation can only happen at init, when
doing buffer reallocation after init, care must be taken
care of memory which priv_buf points to.
This patch fixes it by using a dynamic allocated temporary
memory. Because we only do buffer reallocation at init or
when setting up the DCB parameter, and priv_buf is only
used at buffer allocation process, so it is ok to use a
dynamic allocated temporary memory.

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