openvswitch: Move dev pointer into vport itself

This is the first step in representing all OVS vports as regular
struct net_devices. Move the net_device pointer into the vport
structure itself to get rid of struct vport_netdev.

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