net: airoha: Fix TSO support for header cloned skbs

For GSO packets, skb_cow_head() will reallocate the skb for TSO header
cloned skbs in airoha_dev_xmit(). For this reason, sinfo pointer can be
no more valid. Fix the issue relying on skb_shinfo() macro directly in
airoha_dev_xmit().

The problem exists since
commit 23020f04 ("net: airoha: Introduce ethernet support for EN7581 SoC")
but it is not a user visible, since we can't currently enable TSO
for DSA user ports since we are missing to initialize net_device
vlan_features field.

Reviewed-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250213-airoha-en7581-flowtable-offload-v4-1-b69ca16d74db@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>