net/packet: fix packet receive on L3 devices without visible hard header

In the patchset merged by commit b9fcf0a0d826
("Merge branch 'support-AF_PACKET-for-layer-3-devices'") L3 devices which
did not have header_ops were given one for the purpose of protocol parsing
on af_packet transmit path.

That change made af_packet receive path regard these devices as having a
visible L3 header and therefore aligned incoming skb->data to point to the
skb's mac_header. Some devices, such as ipip, xfrmi, and others, do not
reset their mac_header prior to ingress and therefore their incoming
packets became malformed.

Ideally these devices would reset their mac headers, or af_packet would be
able to rely on dev->hard_header_len being 0 for such cases, but it seems
this is not the case.

Fix by changing af_packet RX ll visibility criteria to include the
existence of a '.create()' header operation, which is used when creating
a device hard header - via dev_hard_header() - by upper layers, and does
not exist in these L3 devices.

As this predicate may be useful in other situations, add it as a common
dev_has_header() helper in netdevice.h.

Fixes: b9fcf0a0d826 ("Merge branch 'support-AF_PACKET-for-layer-3-devices'")
Signed-off-by: Eyal Birger <[email protected]>
Acked-by: Jason A. Donenfeld <[email protected]>
Acked-by: Willem de Bruijn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

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