gve: Add a jumbo-frame device option.

A widely deployed driver has a bug that will cause the driver not
to load when a max_mtu > 2048 is present in the device descriptor.

To avoid this bug while still enabling jumbo frames, we present a lower
max_mtu in the device descriptor and pass the actual max_mtu in
a separate device option.

The driver supports 2 different queue formats. To enable features
on one queue format, but not the other, a supported_features mask
was added to the device options in the device descriptor.

Signed-off-by: Shailend Chand <shailend@google.com>
Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>