net/mlx5e: Use skb_shinfo(skb)->gso_segs rather than counting them

Instead of counting number of gso fragments, we can use
skb_shinfo(skb)->gso_segs.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>