Merge branch 'virtio-net-fix-for-virtio_net_f_guest_hdrlen'

Xuan Zhuo says:

====================
virtio-net: fix for VIRTIO_NET_F_GUEST_HDRLEN

The commit be50da3e9d4a ("net: virtio_net: implement exact header length
guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN
feature in virtio-net.

This feature requires virtio-net to set hdr_len to the actual header
length of the packet when transmitting, the number of
bytes from the start of the packet to the beginning of the
transport-layer payload.

However, in practice, hdr_len was being set using skb_headlen(skb),
which is clearly incorrect. This path set fixes that issue.

As discussed in [0], this version checks the VIRTIO_NET_F_GUEST_HDRLEN is
negotiated.

[0]: http://lore.kernel.org/all/20251029030913.20423-1-xuanzhuo@linux.alibaba.com

v10: fix http://lore.kernel.org/all/202603122214.8Anoxrmq-lkp@intel.com
====================

Link: https://patch.msgid.link/20260320021818.111741-1-xuanzhuo@linux.alibaba.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>