If is_ptp_ring == true in the loop of __aq_ring_xdp_clean function,
then a timestamp is stored from a packet in a field of skb object,
which is not allocated at the moment of the call (skb == NULL).

Generalize aq_ptp_extract_ts and other affected functions so they don't
work with struct sk_buff*, but with struct skb_shared_hwtstamps*.

Found by Linux Verification Center (linuxtesting.org) with SVACE

Fixes: 26efaef7 ("net: atlantic: Implement xdp data plane")
Signed-off-by: Daniil Maximov <daniil31415it@gmail.com>
Reviewed-by: Igor Russkikh <irusskikh@marvell.com>
Link: https://lore.kernel.org/r/20231204085810.1681386-1-daniil31415it@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>