net: Disable segmentation if checksumming is not supported

In the case of the mlx4 and mlx5 driver they do not support IPv6 checksum
offload for tunnels.  With this being the case we should disable GSO in
addition to the checksum offload features when we find that a device cannot
perform a checksum on a given packet type.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>