Re: [PATCH net] amt: do not offer software GSO on the amt device

Found by code inspection: an LLM-assisted review of drivers/net/amt.c
while I was working on an IPv6 outer transport for amt.

It has not been triggered. I have no reproducer, and I have not seen
it in production or in testing; it comes from reading the code. The
path is a GSO skb, for example from a UDP_SEGMENT sender or a GRO
merged UDP flow, that is routed to a relay's amt device: it reaches
amt_dev_xmit() unsegmented because the device offers
NETIF_F_GSO_SOFTWARE, and the outer UDP layer later segments each
per-tunnel copy at the inner gso_size.

Testing: W=1 build with CONFIG_IPV6=y and =n, and
tools/testing/selftests/net/amt.sh passes with the patch applied, but
amt.sh never sends a GSO skb, so nothing exercises the changed path.