virtio-net: fix incorrect flags recording in big mode

virtio-net: fix incorrect flags recording in big mode

The purpose of commit 703eec1b2422 ("virtio_net: fixing XDP for fully
checksummed packets handling") is to record the flags in advance, as
their value may be overwritten in the XDP case. However, the flags
recorded under big mode are incorrect, because in big mode, the passed
buf does not point to the rx buffer, but rather to the page of the
submitted buffer. This commit fixes this issue.

For the small mode, the commit c11a49d58ad2 ("virtio_net: Fix mismatched
buf address when unmapping for small packets") fixed it.

Tested-by: Alyssa Ross <hi@alyssa.is>
Fixes: 703eec1b2422 ("virtio_net: fixing XDP for fully checksummed packets handling")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20251111090828.23186-1-xuanzhuo@linux.alibaba.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>