selftests/net: remove min gso test in packet_snd

This patch removed the 'raw gso min size - 1' test which
always fails now:
./in_netns.sh ./psock_snd -v -c -g -l "${mss}"
  raw gso min size - 1 (expected to fail)
  tx: 1524
  rx: 1472
  OK

After commit 7c6d2ecb ("net: be more gentle about silly
gso requests coming from user"), we relaxed the min gso_size
check in virtio_net_hdr_to_skb().
So when a packet which is smaller then the gso_size,
GSO for this packet will not be set, the packet will be
send/recv successfully.

Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>