openvswitch: Use Geneve device.

With help of tunnel metadata mode OVS can directly use
Geneve devices to implement Geneve tunnels.
This patch removes all of the OVS specific Geneve code
and make OVS use a Geneve net_device. Basic geneve vport
is still there to handle compatibility with current
userspace application.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Reviewed-by: Jesse Gross <jesse@nicira.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>