Currently, the kernel drops GSO VLAN tagged packet if it's created with
socket(AF_PACKET, SOCK_RAW, 0) plus virtio_net_hdr.

The reason is AF_PACKET doesn't adjust the skb network header if there is
a VLAN tag. Then after virtio_net_hdr_set_proto() called, the skb->protocol
will be set to ETH_P_IP/IPv6. And in later inet/ipv6_gso_segment() the skb
is dropped as network header position is invalid.

Let's handle VLAN packets by adjusting network header position in
packet_parse_headers(). The adjustment is safe and does not affect the
later xmit as tap device also did that.

In packet_snd(), packet_parse_headers() need to be moved before calling
virtio_net_hdr_set_proto(), so we can set correct skb->protocol and
network header first.

There is no need to update tpacket_snd() as it calls packet_parse_headers()
in tpacket_fill_skb(), which is already before calling virtio_net_hdr_*
functions.

skb->no_fcs setting is also moved upper to make all skb settings together
and keep consistency with function packet_sendmsg_spkt().
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20220425014502.985464-1-liuhangbin@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>