Revert "virtio-net: Copy received header to buffer"

Revert "virtio-net: Copy received header to buffer"

This reverts commit 7987d2be5a8bc3a502f89ba8cf3ac3e09f64d1ce.

The goal was to remove the need to patch the (const) input buffer
with a recomputed UDP checksum by copying headers to a RW region and
inject the checksum there. The patch computed the checksum only from the
header fields (missing the rest of the payload) producing an invalid one
and making guests fail to acquire a DHCP lease.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2727
Cc: qemu-stable@nongnu.org
Signed-off-by: Antoine Damhet <adamhet@scaleway.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250408145345.142947-1-adamhet@scaleway.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit e28fbd1c525db21f0502b85517f49504c9f9dcd8)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>