net: Fix inet checksum regressions.

JIRA: https://issues.redhat.com/browse/RHEL-62411 Upstream Status: linux.git

Backporting upstream commit 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr") created some regressions that have now been fixed upstream. We need to backport those fixes too.

Signed-off-by: Guillaume Nault gnault@redhat.com