net/hns3: fix HW buffer size on MTU update

net/hns3: fix HW buffer size on MTU update

After MTU changed, the buffer used to store packets in HW should be
reallocated. And buffer size is allocated based on the maximum frame
size in the PF struct. However, the value of maximum frame size  is
not updated in time when MTU is changed. This would lead to a packet
loss for not enough buffer.

This patch update the maximum frame size before reallocating the HW
buffer. And a rollback operation is added to avoid the side effects
of buffer reallocation failures.

Fixes: 1f5ca0b460cd ("net/hns3: support some device operations")
Fixes: d51867db65c1 ("net/hns3: add initialization")
Cc: stable@dpdk.org
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>