net: ethtool: add missing NETIF_F_GSO_FRAGLIST feature string

Commit 3b335832 ("net: Add fraglist GRO/GSO feature flags") missed
an entry for NETIF_F_GSO_FRAGLIST in netdev_features_strings array. As
a result, fraglist GSO feature is not shown in 'ethtool -k' output and
can't be toggled on/off.
The fix is trivial.

Fixes: 3b335832 ("net: Add fraglist GRO/GSO feature flags")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>